v2.4.0.6
Consolidated Condensed Schedule Of Investments (Long Investments) (USD $)
In Thousands, unless otherwise specified
 9 Months Ended 12 Months Ended
Sep. 30, 2012
Dec. 31, 2011
Schedule of Investments [Line Items]    
Fair Value $ 1,165,644 $ 1,212,483
Investments at value, cost 1,133,991 1,234,203
U.S. Treasury Securities [Member]
    
Schedule of Investments [Line Items]    
Long investment holdings as a percentage of shareholders' equity   2.72%
Unrated But Agency-Guaranteed [Member]
    
Schedule of Investments [Line Items]    
Long investment holdings as a percentage of shareholders' equity 131.13% 206.07%
Long Investment AAA Rating [Member]
    
Schedule of Investments [Line Items]    
Long investment holdings as a percentage of shareholders' equity 0.02% 1.25%
Long Investment AA Rating [Member]
    
Schedule of Investments [Line Items]    
Long investment holdings as a percentage of shareholders' equity 0.45% 1.88%
Long Investment A Rating [Member]
    
Schedule of Investments [Line Items]    
Long investment holdings as a percentage of shareholders' equity 1.85% 5.44%
Long Investment BBB Rating [Member]
    
Schedule of Investments [Line Items]    
Long investment holdings as a percentage of shareholders' equity 8.25% 3.46%
Long Investment BB Rating [Member]
    
Schedule of Investments [Line Items]    
Long investment holdings as a percentage of shareholders' equity 90.44% 103.36%
Long Investment Unrated Rating [Member]
    
Schedule of Investments [Line Items]    
Long investment holdings as a percentage of shareholders' equity 1.62% 2.71%
Long Investments [Member]
    
Schedule of Investments [Line Items]    
Investments owned as a percentage of net assets 233.76% [1],[2] 326.89% [1],[3]
Fair Value 1,165,644 [1],[2] 1,212,483 [1],[3]
Investments at value, cost 1,133,991 [1],[2] 1,234,203 [1],[3]
Long Investments [Member] | Federal Home Loan Mortgage Corporation [Member]
    
Schedule of Investments [Line Items]    
Investments owned as a percentage of net assets 25.88% 63.62%
Long Investments [Member] | Government National Mortgage Association [Member]
    
Schedule of Investments [Line Items]    
Investments owned as a percentage of net assets 0.67% 0.41%
Long Investments [Member] | Federal National Mortgage Association [Member]
    
Schedule of Investments [Line Items]    
Investments owned as a percentage of net assets 104.58% 142.04%
Mortgage-Backed Securities [Member]
    
Schedule of Investments [Line Items]    
Investments owned as a percentage of net assets 232.83% [1],[2] 322.98% [1],[3]
Fair Value 1,160,994 [1],[2] 1,197,970 [1],[3]
Investments at value, cost 1,129,131 [1],[2] 1,219,423 [1],[3]
Agency Securities [Member]
    
Schedule of Investments [Line Items]    
Investments owned as a percentage of net assets 131.13% [1],[2],[4] 206.07% [1],[3],[5]
Fair Value 653,873 [1],[2],[4] 764,344 [1],[3],[5]
Investments at value, cost 642,123 [1],[2],[4] 755,771 [1],[3],[5]
Fixed Rate Agency Securities [Member]
    
Schedule of Investments [Line Items]    
Investments owned as a percentage of net assets 127.00% [1],[2],[4] 195.78% [1],[3],[5]
Fair Value 633,290 [1],[2],[4] 726,160 [1],[3],[5]
Investments at value, cost 622,122 [1],[2],[4] 718,177 [1],[3],[5]
Principal And Interest - Fixed Rate Agency Securities [Member]
    
Schedule of Investments [Line Items]    
Investments owned as a percentage of net assets 119.50% [1],[2],[4] 185.76% [1],[3],[5]
Fair Value 595,906 [1],[2],[4] 689,018 [1],[3],[5]
Principal And Interest - Fixed Rate Agency Securities [Member] | 22,536 Federal National Mortgage Association Pool 4.50% 2041-12 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount 22,536 [1],[2],[4]  
Description Federal National Mortgage Association Pool [1],[2],[4]  
Rate 4.50% [1],[2],[4]  
Maturity 2041-12 [1],[2],[4]  
Fair Value 24,622 [1],[2],[4]  
Principal And Interest - Fixed Rate Agency Securities [Member] | 20,826 Federal National Mortgage Association Pool 3.50% 2042-09 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount 20,826 [1],[2],[4]  
Description Federal National Mortgage Association Pool [1],[2],[4]  
Rate 3.50% [1],[2],[4]  
Maturity 2042-09 [1],[2],[4]  
Fair Value 22,399 [1],[2],[4]  
Principal And Interest - Fixed Rate Agency Securities [Member] | Federal National Mortgage Association Pool 5.00% 2035-10 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount 18,522 [1],[2],[4]  
Description Federal National Mortgage Association Pool [1],[2],[4]  
Rate 5.00% [1],[2],[4]  
Maturity 2035-10 [1],[2],[4]  
Fair Value 20,213 [1],[2],[4]  
Principal And Interest - Fixed Rate Agency Securities [Member] | Federal National Mortgage Association Pool 5.00% 2041-08 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount 18,241 [1],[2],[4]  
Description Federal National Mortgage Association Pool [1],[2],[4]  
Rate 5.00% [1],[2],[4]  
Maturity 2041-08 [1],[2],[4]  
Fair Value 20,012 [1],[2],[4]  
Principal And Interest - Fixed Rate Agency Securities [Member] | 18,327 Federal National Mortgage Association Pool 3.50% 2042-08 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount 18,327 [1],[2],[4]  
Description Federal National Mortgage Association Pool [1],[2],[4]  
Rate 3.50% [1],[2],[4]  
Maturity 2042-08 [1],[2],[4]  
Fair Value 19,735 [1],[2],[4]  
Principal And Interest - Fixed Rate Agency Securities [Member] | 17,926 Federal National Mortgage Association Pool 4.50% 2041-09 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount 17,926 [1],[2],[4]  
Description Federal National Mortgage Association Pool [1],[2],[4]  
Rate 4.50% [1],[2],[4]  
Maturity 2041-09 [1],[2],[4]  
Fair Value 19,585 [1],[2],[4]  
Principal And Interest - Fixed Rate Agency Securities [Member] | 17,637 Federal National Mortgage Association Pool 4.50% 2041-10 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount 17,637 [1],[2],[4]  
Description Federal National Mortgage Association Pool [1],[2],[4]  
Rate 4.50% [1],[2],[4]  
Maturity 2041-10 [1],[2],[4]  
Fair Value 19,270 [1],[2],[4]  
Principal And Interest - Fixed Rate Agency Securities [Member] | 15,981 Federal National Mortgage Association Pool 4.50% 2041-09 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount 15,981 [1],[2],[4]  
Description Federal National Mortgage Association Pool [1],[2],[4]  
Rate 4.50% [1],[2],[4]  
Maturity 2041-09 [1],[2],[4]  
Fair Value 17,361 [1],[2],[4]  
Principal And Interest - Fixed Rate Agency Securities [Member] | 13,603 Federal National Mortgage Association Pool 3.50% 2042-08 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount 13,603 [1],[2],[4]  
Description Federal National Mortgage Association Pool [1],[2],[4]  
Rate 3.50% [1],[2],[4]  
Maturity 2042-08 [1],[2],[4]  
Fair Value 14,648 [1],[2],[4]  
Principal And Interest - Fixed Rate Agency Securities [Member] | 12,393 Federal National Mortgage Association Pool 4.50% 2041-09 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount 12,393 [1],[2],[4]  
Description Federal National Mortgage Association Pool [1],[2],[4]  
Rate 4.50% [1],[2],[4]  
Maturity 2041-09 [1],[2],[4]  
Fair Value 13,463 [1],[2],[4]  
Principal And Interest - Fixed Rate Agency Securities [Member] | 11,663 Federal National Mortgage Association Pool 5.00% 2041-07 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount 11,663 [1],[2],[4]  
Description Federal National Mortgage Association Pool [1],[2],[4]  
Rate 5.00% [1],[2],[4]  
Maturity 2041-07 [1],[2],[4]  
Fair Value 12,868 [1],[2],[4]  
Principal And Interest - Fixed Rate Agency Securities [Member] | Federal Home Loan Mortgage Corporation Pool 3.50% 2042-08 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount 11,524 [1],[2],[4]  
Description Federal Home Loan Mortgage Corporation Pool [1],[2],[4]  
Rate 3.50% [1],[2],[4]  
Maturity 2042-08 [1],[2],[4]  
Fair Value 12,469 [1],[2],[4]  
Principal And Interest - Fixed Rate Agency Securities [Member] | Federal National Mortgage Association Pool 4.00% 2042-01 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount 10,956 [1],[2],[4]  
Description Federal National Mortgage Association Pool [1],[2],[4]  
Rate 4.00% [1],[2],[4]  
Maturity 2042-01 [1],[2],[4]  
Fair Value 11,822 [1],[2],[4]  
Principal And Interest - Fixed Rate Agency Securities [Member] | Federal National Mortgage Association Pool 3.50% 2042-09 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount 9,599 [1],[2],[4]  
Description Federal National Mortgage Association Pool [1],[2],[4]  
Rate 3.50% [1],[2],[4]  
Maturity 2042-09 [1],[2],[4]  
Fair Value 10,336 [1],[2],[4]  
Principal And Interest - Fixed Rate Agency Securities [Member] | Federal National Mortgage Association Pool 3.00% 2027-08 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount 8,778 [1],[2],[4]  
Description Federal National Mortgage Association Pool [1],[2],[4]  
Rate 3.00% [1],[2],[4]  
Maturity 2027-08 [1],[2],[4]  
Fair Value 9,311 [1],[2],[4]  
Principal And Interest - Fixed Rate Agency Securities [Member] | Federal National Mortgage Association Pool 3.00% 2027-09 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount 7,097 [1],[2],[4]  
Description Federal National Mortgage Association Pool [1],[2],[4]  
Rate 3.00% [1],[2],[4]  
Maturity 2027-09 [1],[2],[4]  
Fair Value 7,529 [1],[2],[4]  
Principal And Interest - Fixed Rate Agency Securities [Member] | Federal National Mortgage Association Pool 5.00% 2041-06 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount 6,575 [1],[2],[4]  
Description Federal National Mortgage Association Pool [1],[2],[4]  
Rate 5.00% [1],[2],[4]  
Maturity 2041-06 [1],[2],[4]  
Fair Value 7,213 [1],[2],[4]  
Principal And Interest - Fixed Rate Agency Securities [Member] | Federal National Mortgage Association Pool 5.00% 2034-03 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount 6,141 [1],[2],[4]  
Description Federal National Mortgage Association Pool [1],[2],[4]  
Rate 5.00% [1],[2],[4]  
Maturity 2034-03 [1],[2],[4]  
Fair Value 6,734 [1],[2],[4]  
Principal And Interest - Fixed Rate Agency Securities [Member] | Federal Home Loan Mortgage Corporation Pool 4.00% 2042-05 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount 5,989 [1],[2],[4]  
Description Federal Home Loan Mortgage Corporation Pool [1],[2],[4]  
Rate 4.00% [1],[2],[4]  
Maturity 2042-05 [1],[2],[4]  
Fair Value 6,509 [1],[2],[4]  
Principal And Interest - Fixed Rate Agency Securities [Member] | Federal National Mortgage Association Pool 5.00% 2041-07 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount 5,864 [1],[2],[4]  
Description Federal National Mortgage Association Pool [1],[2],[4]  
Rate 5.00% [1],[2],[4]  
Maturity 2041-07 [1],[2],[4]  
Fair Value 6,396 [1],[2],[4]  
Principal And Interest - Fixed Rate Agency Securities [Member] | Federal National Mortgage Association Pool 5.00% 2039-11 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount 5,698 [1],[2],[4]  
Description Federal National Mortgage Association Pool [1],[2],[4]  
Rate 5.00% [1],[2],[4]  
Maturity 2039-11 [1],[2],[4]  
Fair Value 6,215 [1],[2],[4]  
Principal And Interest - Fixed Rate Agency Securities [Member] | Federal National Mortgage Association Pool 4.00% 2041-10 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount 5,615 [1],[2],[4]  
Description Federal National Mortgage Association Pool [1],[2],[4]  
Rate 4.00% [1],[2],[4]  
Maturity 2041-10 [1],[2],[4]  
Fair Value 6,092 [1],[2],[4]  
Principal And Interest - Fixed Rate Agency Securities [Member] | Federal National Mortgage Association Pool 5.00% 2041-10 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount 5,502 [1],[2],[4]  
Description Federal National Mortgage Association Pool [1],[2],[4]  
Rate 5.00% [1],[2],[4]  
Maturity 2041-10 [1],[2],[4]  
Fair Value 6,029 [1],[2],[4]  
Principal And Interest - Fixed Rate Agency Securities [Member] | 5,550 Federal National Mortgage Association Pool 3.50% 2042-11 (Pre-Issue) [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount 5,550 [1],[2],[4]  
Description Federal National Mortgage Association Pool (Pre-Issue) [1],[2],[4]  
Rate 3.50% [1],[2],[4]  
Maturity 2042-11 [1],[2],[4]  
Fair Value 6,004 [1],[2],[4]  
Principal And Interest - Fixed Rate Agency Securities [Member] | 5,569 Federal National Mortgage Association Pool 3.50% 2042-08 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount 5,569 [1],[2],[4]  
Description Federal National Mortgage Association Pool [1],[2],[4]  
Rate 3.50% [1],[2],[4]  
Maturity 2042-08 [1],[2],[4]  
Fair Value 5,974 [1],[2],[4]  
Principal And Interest - Fixed Rate Agency Securities [Member] | Federal Home Loan Mortgage Corporation Pool 3.50% 2042-09 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount 5,240 [1],[2],[4]  
Description Federal Home Loan Mortgage Corporation Pool [1],[2],[4]  
Rate 3.50% [1],[2],[4]  
Maturity 2042-09 [1],[2],[4]  
Fair Value 5,654 [1],[2],[4]  
Principal And Interest - Fixed Rate Agency Securities [Member] | 5,108 Federal National Mortgage Association Pool 4.00% 2042-04 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount 5,108 [1],[2],[4]  
Description Federal National Mortgage Association Pool [1],[2],[4]  
Rate 4.00% [1],[2],[4]  
Maturity 2042-04 [1],[2],[4]  
Fair Value 5,567 [1],[2],[4]  
Principal And Interest - Fixed Rate Agency Securities [Member] | Federal National Mortgage Association Pool 3.50% 2042-07 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount 4,748 [1],[2],[4]  
Description Federal National Mortgage Association Pool [1],[2],[4]  
Rate 3.50% [1],[2],[4]  
Maturity 2042-07 [1],[2],[4]  
Fair Value 5,093 [1],[2],[4]  
Principal And Interest - Fixed Rate Agency Securities [Member] | Federal National Mortgage Association Pool 5.00% 2041-09 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount 4,450 [1],[2],[4]  
Description Federal National Mortgage Association Pool [1],[2],[4]  
Rate 5.00% [1],[2],[4]  
Maturity 2041-09 [1],[2],[4]  
Fair Value 4,931 [1],[2],[4]  
Principal And Interest - Fixed Rate Agency Securities [Member] | Federal Home Loan Mortgage Corporation Pool 3.50% 2042-10 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount 4,522 [1],[2],[4]  
Description Federal Home Loan Mortgage Corporation Pool [1],[2],[4]  
Rate 3.50% [1],[2],[4]  
Maturity 2042-10 [1],[2],[4]  
Fair Value 4,847 [1],[2],[4]  
Principal And Interest - Fixed Rate Agency Securities [Member] | Federal Home Loan Mortgage Corporation Pool 4.00% 2042-02 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount 4,487 [1],[2],[4]  
Description Federal Home Loan Mortgage Corporation Pool [1],[2],[4]  
Rate 4.00% [1],[2],[4]  
Maturity 2042-02 [1],[2],[4]  
Fair Value 4,844 [1],[2],[4]  
Principal And Interest - Fixed Rate Agency Securities [Member] | 4,418 Federal National Mortgage Association Pool 3.50% 2042-08 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount 4,418 [1],[2],[4]  
Description Federal National Mortgage Association Pool [1],[2],[4]  
Rate 3.50% [1],[2],[4]  
Maturity 2042-08 [1],[2],[4]  
Fair Value 4,740 [1],[2],[4]  
Principal And Interest - Fixed Rate Agency Securities [Member] | 4,330 Federal National Mortgage Association Pool 3.50% 2027-06 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount 4,330 [1],[2],[4]  
Description Federal National Mortgage Association Pool [1],[2],[4]  
Rate 3.50% [1],[2],[4]  
Maturity 2027-06 [1],[2],[4]  
Fair Value 4,640 [1],[2],[4]  
Principal And Interest - Fixed Rate Agency Securities [Member] | Federal Home Loan Mortgage Corporation Pool 4.00% 2041-11 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount 4,087 [1],[2],[4]  
Description Federal Home Loan Mortgage Corporation Pool [1],[2],[4]  
Rate 4.00% [1],[2],[4]  
Maturity 2041-11 [1],[2],[4]  
Fair Value 4,416 [1],[2],[4]  
Principal And Interest - Fixed Rate Agency Securities [Member] | 3,923 Federal National Mortgage Association Pool 4.50% 2041-12 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount 3,923 [1],[2],[4]  
Description Federal National Mortgage Association Pool [1],[2],[4]  
Rate 4.50% [1],[2],[4]  
Maturity 2041-12 [1],[2],[4]  
Fair Value 4,261 [1],[2],[4]  
Principal And Interest - Fixed Rate Agency Securities [Member] | 3,946 Federal National Mortgage Association Pool 3.50% 2042-08 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount 3,946 [1],[2],[4]  
Description Federal National Mortgage Association Pool [1],[2],[4]  
Rate 3.50% [1],[2],[4]  
Maturity 2042-08 [1],[2],[4]  
Fair Value 4,234 [1],[2],[4]  
Principal And Interest - Fixed Rate Agency Securities [Member] | Federal National Mortgage Association Pool 4.50% 2042-04 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount 3,778 [1],[2],[4]  
Description Federal National Mortgage Association Pool [1],[2],[4]  
Rate 4.50% [1],[2],[4]  
Maturity 2042-04 [1],[2],[4]  
Fair Value 4,137 [1],[2],[4]  
Principal And Interest - Fixed Rate Agency Securities [Member] | 3,812 Federal National Mortgage Association Pool 3.50% 2027-06 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount 3,812 [1],[2],[4]  
Description Federal National Mortgage Association Pool [1],[2],[4]  
Rate 3.50% [1],[2],[4]  
Maturity 2027-06 [1],[2],[4]  
Fair Value 4,085 [1],[2],[4]  
Principal And Interest - Fixed Rate Agency Securities [Member] | Federal National Mortgage Association Pool 4.50% 2041-11 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount 3,676 [1],[2],[4]  
Description Federal National Mortgage Association Pool [1],[2],[4]  
Rate 4.50% [1],[2],[4]  
Maturity 2041-11 [1],[2],[4]  
Fair Value 3,994 [1],[2],[4]  
Principal And Interest - Fixed Rate Agency Securities [Member] | Federal Home Loan Mortgage Corporation Pool 4.00% 2042-01 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount 3,691 [1],[2],[4]  
Description Federal Home Loan Mortgage Corporation Pool [1],[2],[4]  
Rate 4.00% [1],[2],[4]  
Maturity 2042-01 [1],[2],[4]  
Fair Value 3,989 [1],[2],[4]  
Principal And Interest - Fixed Rate Agency Securities [Member] | 3,644 Federal National Mortgage Association Pool 3.50% 2042-11 (Pre-Issue) [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount 3,644 [1],[2],[4]  
Description Federal National Mortgage Association Pool (Pre-Issue) [1],[2],[4]  
Rate 3.50% [1],[2],[4]  
Maturity 2042-11 [1],[2],[4]  
Fair Value 3,964 [1],[2],[4]  
Principal And Interest - Fixed Rate Agency Securities [Member] | 3,435 Federal National Mortgage Association Pool 4.00% 2042-04 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount 3,435 [1],[2],[4]  
Description Federal National Mortgage Association Pool [1],[2],[4]  
Rate 4.00% [1],[2],[4]  
Maturity 2042-04 [1],[2],[4]  
Fair Value 3,742 [1],[2],[4]  
Principal And Interest - Fixed Rate Agency Securities [Member] | Federal Home Loan Mortgage Corporation Pool 3.50% 2042-02 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount 3,307 [1],[2],[4]  
Description Federal Home Loan Mortgage Corporation Pool [1],[2],[4]  
Rate 3.50% [1],[2],[4]  
Maturity 2042-02 [1],[2],[4]  
Fair Value 3,561 [1],[2],[4]  
Principal And Interest - Fixed Rate Agency Securities [Member] | 3,236 Federal National Mortgage Association Pool 4.50% 2041-10 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount 3,236 [1],[2],[4]  
Description Federal National Mortgage Association Pool [1],[2],[4]  
Rate 4.50% [1],[2],[4]  
Maturity 2041-10 [1],[2],[4]  
Fair Value 3,526 [1],[2],[4]  
Principal And Interest - Fixed Rate Agency Securities [Member] | 3,196 Federal National Mortgage Association Pool 4.00% 2042-08 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount 3,196 [1],[2],[4]  
Description Federal National Mortgage Association Pool [1],[2],[4]  
Rate 4.00% [1],[2],[4]  
Maturity 2042-08 [1],[2],[4]  
Fair Value 3,473 [1],[2],[4]  
Principal And Interest - Fixed Rate Agency Securities [Member] | 2,943 Federal National Mortgage Association Pool 4.00% 2042-08 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount 2,943 [1],[2],[4]  
Description Federal National Mortgage Association Pool [1],[2],[4]  
Rate 4.00% [1],[2],[4]  
Maturity 2042-08 [1],[2],[4]  
Fair Value 3,206 [1],[2],[4]  
Principal And Interest - Fixed Rate Agency Securities [Member] | Federal National Mortgage Association Pool 3.50% 2027-07 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount 2,995 [1],[2],[4]  
Description Federal National Mortgage Association Pool [1],[2],[4]  
Rate 3.50% [1],[2],[4]  
Maturity 2027-07 [1],[2],[4]  
Fair Value 3,205 [1],[2],[4]  
Principal And Interest - Fixed Rate Agency Securities [Member] | Government National Mortgage Association (Pre-Issue) 4.49% 2042-09 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount 2,700 [1],[2],[4]  
Description Government National Mortgage Association (Pre-Issue) [1],[2],[4]  
Rate 4.49% [1],[2],[4]  
Maturity 2042-09 [1],[2],[4]  
Fair Value 3,074 [1],[2],[4]  
Principal And Interest - Fixed Rate Agency Securities [Member] | 2,687 Federal National Mortgage Association Pool 4.50% 2041-10 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount 2,687 [1],[2],[4]  
Description Federal National Mortgage Association Pool [1],[2],[4]  
Rate 4.50% [1],[2],[4]  
Maturity 2041-10 [1],[2],[4]  
Fair Value 2,919 [1],[2],[4]  
Principal And Interest - Fixed Rate Agency Securities [Member] | Federal National Mortgage Association Pool 3.50% 2042-05 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount 2,640 [1],[2],[4]  
Description Federal National Mortgage Association Pool [1],[2],[4]  
Rate 3.50% [1],[2],[4]  
Maturity 2042-05 [1],[2],[4]  
Fair Value 2,832 [1],[2],[4]  
Principal And Interest - Fixed Rate Agency Securities [Member] | 2,576 Federal National Mortgage Association Pool 4.00% 2042-08 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount 2,576 [1],[2],[4]  
Description Federal National Mortgage Association Pool [1],[2],[4]  
Rate 4.00% [1],[2],[4]  
Maturity 2042-08 [1],[2],[4]  
Fair Value 2,798 [1],[2],[4]  
Principal And Interest - Fixed Rate Agency Securities [Member] | Federal National Mortgage Association Pool 4.00% 2042-09 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount 2,508 [1],[2],[4]  
Description Federal National Mortgage Association Pool [1],[2],[4]  
Rate 4.00% [1],[2],[4]  
Maturity 2042-09 [1],[2],[4]  
Fair Value 2,725 [1],[2],[4]  
Principal And Interest - Fixed Rate Agency Securities [Member] | Federal Home Loan Mortgage Corporation Pool 3.50% 2042-01 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount 2,516 [1],[2],[4]  
Description Federal Home Loan Mortgage Corporation Pool [1],[2],[4]  
Rate 3.50% [1],[2],[4]  
Maturity 2042-01 [1],[2],[4]  
Fair Value 2,703 [1],[2],[4]  
Principal And Interest - Fixed Rate Agency Securities [Member] | 2,509 Federal National Mortgage Association Pool 3.50% 2042-08 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount 2,509 [1],[2],[4]  
Description Federal National Mortgage Association Pool [1],[2],[4]  
Rate 3.50% [1],[2],[4]  
Maturity 2042-08 [1],[2],[4]  
Fair Value 2,701 [1],[2],[4]  
Principal And Interest - Fixed Rate Agency Securities [Member] | 85,000 Federal Home Loan Mortgage Corporation Pool 4.50% 2041-10 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount   85,000 [1],[3],[5]
Description   Federal Home Loan Mortgage Corporation Pool [1],[3],[5]
Rate   4.50% [1],[3],[5]
Maturity   2041-10 [1],[3],[5]
Fair Value   90,611 [1],[3],[5]
Principal And Interest - Fixed Rate Agency Securities [Member] | 25,882 Federal National Mortgage Association Pool 5.00% 2041-07 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount   25,882 [1],[3],[5]
Description   Federal National Mortgage Association Pool [1],[3],[5]
Rate   5.00% [1],[3],[5]
Maturity   2041-07 [1],[3],[5]
Fair Value   28,107 [1],[3],[5]
Principal And Interest - Fixed Rate Agency Securities [Member] | Federal Home Loan Mortgage Corporation Pool 4.00% 2040-11 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount   25,456 [1],[3],[5]
Description   Federal Home Loan Mortgage Corporation Pool [1],[3],[5]
Rate   4.00% [1],[3],[5]
Maturity   2040-11 [1],[3],[5]
Fair Value   26,824 [1],[3],[5]
Principal And Interest - Fixed Rate Agency Securities [Member] | Federal National Mortgage Association Pool 4.50% 2041-12 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount   24,164 [1],[3],[5]
Description   Federal National Mortgage Association Pool [1],[3],[5]
Rate   4.50% [1],[3],[5]
Maturity   2041-12 [1],[3],[5]
Fair Value   25,874 [1],[3],[5]
Principal And Interest - Fixed Rate Agency Securities [Member] | 20,212 Federal National Mortgage Association Pool 5.00% 2041-08 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount   20,212 [1],[3],[5]
Description   Federal National Mortgage Association Pool [1],[3],[5]
Rate   5.00% [1],[3],[5]
Maturity   2041-08 [1],[3],[5]
Fair Value   21,937 [1],[3],[5]
Principal And Interest - Fixed Rate Agency Securities [Member] | 18,434 Federal National Mortgage Association Pool 4.50% 2041-09 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount   18,434 [1],[3],[5]
Description   Federal National Mortgage Association Pool [1],[3],[5]
Rate   4.50% [1],[3],[5]
Maturity   2041-09 [1],[3],[5]
Fair Value   19,738 [1],[3],[5]
Principal And Interest - Fixed Rate Agency Securities [Member] | 17,182 Federal National Mortgage Association Pool 4.50% 2041-09 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount   17,182 [1],[3],[5]
Description   Federal National Mortgage Association Pool [1],[3],[5]
Rate   4.50% [1],[3],[5]
Maturity   2041-09 [1],[3],[5]
Fair Value   18,328 [1],[3],[5]
Principal And Interest - Fixed Rate Agency Securities [Member] | Federal Home Loan Mortgage Corporation Pool 5.00% 2039-09 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount   15,465 [1],[3],[5]
Description   Federal Home Loan Mortgage Corporation Pool [1],[3],[5]
Rate   5.00% [1],[3],[5]
Maturity   2039-09 [1],[3],[5]
Fair Value   16,620 [1],[3],[5]
Principal And Interest - Fixed Rate Agency Securities [Member] | 15,243 Federal National Mortgage Association Pool 4.50% 2041-09 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount   15,243 [1],[3],[5]
Description   Federal National Mortgage Association Pool [1],[3],[5]
Rate   4.50% [1],[3],[5]
Maturity   2041-09 [1],[3],[5]
Fair Value   16,260 [1],[3],[5]
Principal And Interest - Fixed Rate Agency Securities [Member] | 14,964 Federal National Mortgage Association Pool 4.50% 2041-11 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount   14,964 [1],[3],[5]
Description   Federal National Mortgage Association Pool [1],[3],[5]
Rate   4.50% [1],[3],[5]
Maturity   2041-11 [1],[3],[5]
Fair Value   15,991 [1],[3],[5]
Principal And Interest - Fixed Rate Agency Securities [Member] | 13,451 Federal National Mortgage Association Pool 4.50% 2041-09 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount   13,451 [1],[3],[5]
Description   Federal National Mortgage Association Pool [1],[3],[5]
Rate   4.50% [1],[3],[5]
Maturity   2041-09 [1],[3],[5]
Fair Value   14,348 [1],[3],[5]
Principal And Interest - Fixed Rate Agency Securities [Member] | 13,033 Federal National Mortgage Association Pool 4.50% 2041-09 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount   13,033 [1],[3],[5]
Description   Federal National Mortgage Association Pool [1],[3],[5]
Rate   4.50% [1],[3],[5]
Maturity   2041-09 [1],[3],[5]
Fair Value   13,927 [1],[3],[5]
Principal And Interest - Fixed Rate Agency Securities [Member] | 13,125 Federal National Mortgage Association Pool 4.00% 2041-10 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount   13,125 [1],[3],[5]
Description   Federal National Mortgage Association Pool [1],[3],[5]
Rate   4.00% [1],[3],[5]
Maturity   2041-10 [1],[3],[5]
Fair Value   13,818 [1],[3],[5]
Principal And Interest - Fixed Rate Agency Securities [Member] | 12,593 Federal National Mortgage Association Pool 5.00% 2041-07 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount   12,593 [1],[3],[5]
Description   Federal National Mortgage Association Pool [1],[3],[5]
Rate   5.00% [1],[3],[5]
Maturity   2041-07 [1],[3],[5]
Fair Value   13,699 [1],[3],[5]
Principal And Interest - Fixed Rate Agency Securities [Member] | 11,095 Federal National Mortgage Association Pool 5.00% 2041-09 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount   11,095 [1],[3],[5]
Description   Federal National Mortgage Association Pool [1],[3],[5]
Rate   5.00% [1],[3],[5]
Maturity   2041-09 [1],[3],[5]
Fair Value   12,098 [1],[3],[5]
Principal And Interest - Fixed Rate Agency Securities [Member] | 10,358 Federal Home Loan Mortgage Corporation Pool 4.00% 2041-01 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount   10,358 [1],[3],[5]
Description   Federal Home Loan Mortgage Corporation Pool [1],[3],[5]
Rate   4.00% [1],[3],[5]
Maturity   2041-01 [1],[3],[5]
Fair Value   10,902 [1],[3],[5]
Principal And Interest - Fixed Rate Agency Securities [Member] | 9,149 Federal Home Loan Mortgage Corporation Pool 4.50% 2041-10 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount   9,149 [1],[3],[5]
Description   Federal Home Loan Mortgage Corporation Pool [1],[3],[5]
Rate   4.50% [1],[3],[5]
Maturity   2041-10 [1],[3],[5]
Fair Value   9,736 [1],[3],[5]
Principal And Interest - Fixed Rate Agency Securities [Member] | 9,027 Federal National Mortgage Association Pool 4.00% 2041-09 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount   9,027 [1],[3],[5]
Description   Federal National Mortgage Association Pool [1],[3],[5]
Rate   4.00% [1],[3],[5]
Maturity   2041-09 [1],[3],[5]
Fair Value   9,498 [1],[3],[5]
Principal And Interest - Fixed Rate Agency Securities [Member] | Federal Home Loan Mortgage Corporation Pool 4.00% 2041-03 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount   8,400 [1],[3],[5]
Description   Federal Home Loan Mortgage Corporation Pool [1],[3],[5]
Rate   4.00% [1],[3],[5]
Maturity   2041-03 [1],[3],[5]
Fair Value   8,851 [1],[3],[5]
Principal And Interest - Fixed Rate Agency Securities [Member] | 8,123 Federal National Mortgage Association Pool 5.00% 2041-09 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount   8,123 [1],[3],[5]
Description   Federal National Mortgage Association Pool [1],[3],[5]
Rate   5.00% [1],[3],[5]
Maturity   2041-09 [1],[3],[5]
Fair Value   8,836 [1],[3],[5]
Principal And Interest - Fixed Rate Agency Securities [Member] | 7,437 Federal National Mortgage Association Pool 5.00% 2041-09 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount   7,437 [1],[3],[5]
Description   Federal National Mortgage Association Pool [1],[3],[5]
Rate   5.00% [1],[3],[5]
Maturity   2041-09 [1],[3],[5]
Fair Value   8,072 [1],[3],[5]
Principal And Interest - Fixed Rate Agency Securities [Member] | Federal National Mortgage Association Pool 4.00% 2026-05 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount   9,152 [1],[3],[5]
Description   Federal National Mortgage Association Pool [1],[3],[5]
Rate   4.00% [1],[3],[5]
Maturity   2026-05 [1],[3],[5]
Fair Value   9,657 [1],[3],[5]
Principal And Interest - Fixed Rate Agency Securities [Member] | Federal Home Loan Mortgage Corporation Pool 5.00% 2041-10 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount   9,995 [1],[3],[5]
Description   Federal Home Loan Mortgage Corporation Pool [1],[3],[5]
Rate   5.00% [1],[3],[5]
Maturity   2041-10 [1],[3],[5]
Fair Value   10,791 [1],[3],[5]
Principal And Interest - Fixed Rate Agency Securities [Member] | Federal National Mortgage Association Pool 4.50% 2041-10 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount   18,120 [1],[3],[5]
Description   Federal National Mortgage Association Pool [1],[3],[5]
Rate   4.50% [1],[3],[5]
Maturity   2041-10 [1],[3],[5]
Fair Value   19,397 [1],[3],[5]
Principal And Interest - Fixed Rate Agency Securities [Member] | Federal Home Loan Mortgage Corporation Pool 5.00% 2041-07 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount 18,146 [1],[2],[4] 18,867 [1],[3],[5]
Description Federal Home Loan Mortgage Corporation Pool [1],[2],[4] Federal Home Loan Mortgage Corporation Pool [1],[3],[5]
Rate 5.00% [1],[2],[4] 5.00% [1],[3],[5]
Maturity 2041-07 [1],[2],[4] 2041-07 [1],[3],[5]
Fair Value 19,894 [1],[2],[4] 20,417 [1],[3],[5]
Principal And Interest - Fixed Rate Agency Securities [Member] | Federal National Mortgage Association Pool 5.00% 2041-03 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount 16,201 [1],[2],[4] 17,391 [1],[3],[5]
Description Federal National Mortgage Association Pool [1],[2],[4] Federal National Mortgage Association Pool [1],[3],[5]
Rate 5.00% [1],[2],[4] 5.00% [1],[3],[5]
Maturity 2041-03 [1],[2],[4] 2041-03 [1],[3],[5]
Fair Value 17,900 [1],[2],[4] 18,941 [1],[3],[5]
Principal And Interest - Fixed Rate Agency Securities [Member] | Federal National Mortgage Association Pool 4.00% 2041-11 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount 12,340 [1],[2],[4] 13,554 [1],[3],[5]
Description Federal National Mortgage Association Pool [1],[2],[4] Federal National Mortgage Association Pool [1],[3],[5]
Rate 4.00% [1],[2],[4] 4.00% [1],[3],[5]
Maturity 2041-11 [1],[2],[4] 2041-11 [1],[3],[5]
Fair Value 13,343 [1],[2],[4] 14,252 [1],[3],[5]
Principal And Interest - Fixed Rate Agency Securities [Member] | Federal National Mortgage Association Pool 4.50% 2026-04 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount 10,112 [1],[2],[4] 11,361 [1],[3],[5]
Description Federal National Mortgage Association Pool [1],[2],[4] Federal National Mortgage Association Pool [1],[3],[5]
Rate 4.50% [1],[2],[4] 4.50% [1],[3],[5]
Maturity 2026-04 [1],[2],[4] 2026-04 [1],[3],[5]
Fair Value 10,943 [1],[2],[4] 12,154 [1],[3],[5]
Principal And Interest - Fixed Rate Agency Securities [Member] | Federal Home Loan Mortgage Corporation Pool 4.50% 2041-02 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount 8,591 [1],[2],[4] 9,176 [1],[3],[5]
Description Federal Home Loan Mortgage Corporation Pool [1],[2],[4] Federal Home Loan Mortgage Corporation Pool [1],[3],[5]
Rate 4.50% [1],[2],[4] 4.50% [1],[3],[5]
Maturity 2041-02 [1],[2],[4] 2041-02 [1],[3],[5]
Fair Value 9,349 [1],[2],[4] 9,805 [1],[3],[5]
Principal And Interest - Fixed Rate Agency Securities [Member] | Federal Home Loan Mortgage Corporation Pool 4.50% 2041-10 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount 9,039 [1],[2],[4]  
Description Federal Home Loan Mortgage Corporation Pool [1],[2],[4]  
Rate 4.50% [1],[2],[4]  
Maturity 2041-10 [1],[2],[4]  
Fair Value 9,837 [1],[2],[4]  
Principal And Interest - Fixed Rate Agency Securities [Member] | Federal National Mortgage Association Pool 4.00% 2026-07 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount 8,169 [1],[2],[4] 9,468 [1],[3],[5]
Description Federal National Mortgage Association Pool [1],[2],[4] Federal National Mortgage Association Pool [1],[3],[5]
Rate 4.00% [1],[2],[4] 4.00% [1],[3],[5]
Maturity 2026-07 [1],[2],[4] 2026-07 [1],[3],[5]
Fair Value 8,745 [1],[2],[4] 10,011 [1],[3],[5]
Principal And Interest - Fixed Rate Agency Securities [Member] | Federal National Mortgage Association Pool 5.50% 2039-10 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount 7,822 [1],[2],[4] 8,468 [1],[3],[5]
Description Federal National Mortgage Association Pool [1],[2],[4] Federal National Mortgage Association Pool [1],[3],[5]
Rate 5.50% [1],[2],[4] 5.50% [1],[3],[5]
Maturity 2039-10 [1],[2],[4] 2039-10 [1],[3],[5]
Fair Value 8,621 [1],[2],[4] 9,269 [1],[3],[5]
Principal And Interest - Fixed Rate Agency Securities [Member] | Federal National Mortgage Association Pool 5.50% 2040-05 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount 5,956 [1],[2],[4] 7,261 [1],[3],[5]
Description Federal National Mortgage Association Pool [1],[2],[4] Federal National Mortgage Association Pool [1],[3],[5]
Rate 5.50% [1],[2],[4] 5.50% [1],[3],[5]
Maturity 2040-05 [1],[2],[4] 2040-05 [1],[3],[5]
Fair Value 6,564 [1],[2],[4] 7,947 [1],[3],[5]
Principal And Interest - Fixed Rate Agency Securities [Member] | 6,955 Federal National Mortgage Association Pool 5.00% 2041-06 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount   6,955 [1],[3],[5]
Description   Federal National Mortgage Association Pool [1],[3],[5]
Rate   5.00% [1],[3],[5]
Maturity   2041-06 [1],[3],[5]
Fair Value   7,553 [1],[3],[5]
Principal And Interest - Fixed Rate Agency Securities [Member] | 6,878 Federal National Mortgage Association Pool 5.00% 2041-07 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount   6,878 [1],[3],[5]
Description   Federal National Mortgage Association Pool [1],[3],[5]
Rate   5.00% [1],[3],[5]
Maturity   2041-07 [1],[3],[5]
Fair Value   7,465 [1],[3],[5]
Principal And Interest - Fixed Rate Agency Securities [Member] | Federal National Mortgage Association Pool 5.00% 2041-05 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount   6,852 [1],[3],[5]
Description   Federal National Mortgage Association Pool [1],[3],[5]
Rate   5.00% [1],[3],[5]
Maturity   2041-05 [1],[3],[5]
Fair Value   7,437 [1],[3],[5]
Principal And Interest - Fixed Rate Agency Securities [Member] | 6,823 Federal National Mortgage Association Pool 5.00% 2041-06 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount   6,823 [1],[3],[5]
Description   Federal National Mortgage Association Pool [1],[3],[5]
Rate   5.00% [1],[3],[5]
Maturity   2041-06 [1],[3],[5]
Fair Value   7,406 [1],[3],[5]
Principal And Interest - Fixed Rate Agency Securities [Member] | 5,836 Federal National Mortgage Association Pool 5.00% 2041-10 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount   5,836 [1],[3],[5]
Description   Federal National Mortgage Association Pool [1],[3],[5]
Rate   5.00% [1],[3],[5]
Maturity   2041-10 [1],[3],[5]
Fair Value   6,334 [1],[3],[5]
Principal And Interest - Fixed Rate Agency Securities [Member] | 5,687 Federal National Mortgage Association Pool 4.00% 2041-10 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount   5,687 [1],[3],[5]
Description   Federal National Mortgage Association Pool [1],[3],[5]
Rate   4.00% [1],[3],[5]
Maturity   2041-10 [1],[3],[5]
Fair Value   5,987 [1],[3],[5]
Principal And Interest - Fixed Rate Agency Securities [Member] | 5,711 Federal National Mortgage Association Pool 3.50% 2041-11 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount   5,711 [1],[3],[5]
Description   Federal National Mortgage Association Pool [1],[3],[5]
Rate   3.50% [1],[3],[5]
Maturity   2041-11 [1],[3],[5]
Fair Value   5,883 [1],[3],[5]
Principal And Interest - Fixed Rate Agency Securities [Member] | Federal Home Loan Mortgage Corporation Pool 4.00% 2041-05 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount   5,549 [1],[3],[5]
Description   Federal Home Loan Mortgage Corporation Pool [1],[3],[5]
Rate   4.00% [1],[3],[5]
Maturity   2041-05 [1],[3],[5]
Fair Value   5,833 [1],[3],[5]
Principal And Interest - Fixed Rate Agency Securities [Member] | 4,888 Federal National Mortgage Association Pool 5.00% 2041-08 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount   4,888 [1],[3],[5]
Description   Federal National Mortgage Association Pool [1],[3],[5]
Rate   5.00% [1],[3],[5]
Maturity   2041-08 [1],[3],[5]
Fair Value   5,330 [1],[3],[5]
Principal And Interest - Fixed Rate Agency Securities [Member] | Federal National Mortgage Association Pool 4.50% 2041-04 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount   4,837 [1],[3],[5]
Description   Federal National Mortgage Association Pool [1],[3],[5]
Rate   4.50% [1],[3],[5]
Maturity   2041-04 [1],[3],[5]
Fair Value   5,190 [1],[3],[5]
Principal And Interest - Fixed Rate Agency Securities [Member] | 4,702 Federal National Mortgage Association Pool 5.00% 2041-09 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount   4,702 [1],[3],[5]
Description   Federal National Mortgage Association Pool [1],[3],[5]
Rate   5.00% [1],[3],[5]
Maturity   2041-09 [1],[3],[5]
Fair Value   5,127 [1],[3],[5]
Principal And Interest - Fixed Rate Agency Securities [Member] | Federal Home Loan Mortgage Corporation Pool 3.50% 2041-10 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount   4,398 [1],[3],[5]
Description   Federal Home Loan Mortgage Corporation Pool [1],[3],[5]
Rate   3.50% [1],[3],[5]
Maturity   2041-10 [1],[3],[5]
Fair Value   4,522 [1],[3],[5]
Principal And Interest - Fixed Rate Agency Securities [Member] | 4,150 Federal National Mortgage Association Pool 5.00% 2041-10 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount   4,150 [1],[3],[5]
Description   Federal National Mortgage Association Pool [1],[3],[5]
Rate   5.00% [1],[3],[5]
Maturity   2041-10 [1],[3],[5]
Fair Value   4,504 [1],[3],[5]
Principal And Interest - Fixed Rate Agency Securities [Member] | 4,230 Federal National Mortgage Association Pool 4.00% 2041-09 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount   4,230 [1],[3],[5]
Description   Federal National Mortgage Association Pool [1],[3],[5]
Rate   4.00% [1],[3],[5]
Maturity   2041-09 [1],[3],[5]
Fair Value   4,454 [1],[3],[5]
Principal And Interest - Fixed Rate Agency Securities [Member] | 4,158 Federal Home Loan Mortgage Corporation Pool 4.00% 2041-01 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount   4,158 [1],[3],[5]
Description   Federal Home Loan Mortgage Corporation Pool [1],[3],[5]
Rate   4.00% [1],[3],[5]
Maturity   2041-01 [1],[3],[5]
Fair Value   4,384 [1],[3],[5]
Principal And Interest - Fixed Rate Agency Securities [Member] | 4,100 Federal National Mortgage Association Pool 4.50% 2041-11 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount   4,100 [1],[3],[5]
Description   Federal National Mortgage Association Pool [1],[3],[5]
Rate   4.50% [1],[3],[5]
Maturity   2041-11 [1],[3],[5]
Fair Value   4,374 [1],[3],[5]
Principal And Interest - Fixed Rate Agency Securities [Member] | 3,751 Federal National Mortgage Association Pool 3.50% 2041-11 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount   3,751 [1],[3],[5]
Description   Federal National Mortgage Association Pool [1],[3],[5]
Rate   3.50% [1],[3],[5]
Maturity   2041-11 [1],[3],[5]
Fair Value   3,859 [1],[3],[5]
Principal And Interest - Fixed Rate Agency Securities [Member] | 2,565 Federal National Mortgage Association Pool 5.00% 2041-07 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount   2,565 [1],[3],[5]
Description   Federal National Mortgage Association Pool [1],[3],[5]
Rate   5.00% [1],[3],[5]
Maturity   2041-07 [1],[3],[5]
Fair Value   2,791 [1],[3],[5]
Principal And Interest - Fixed Rate Agency Securities [Member] | 2,391 Federal National Mortgage Association Pool 5.00% 2041-11 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount   2,391 [1],[3],[5]
Description   Federal National Mortgage Association Pool [1],[3],[5]
Rate   5.00% [1],[3],[5]
Maturity   2041-11 [1],[3],[5]
Fair Value   2,595 [1],[3],[5]
Principal And Interest - Fixed Rate Agency Securities [Member] | Other Federal Home Loan Mortgage Corporation Pool 6.00% 2040-05 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount   1,197 [1],[3],[5]
Description   Other Federal Home Loan Mortgage Corporation Pool [1],[3],[5]
Rate   6.00% [1],[3],[5]
Maturity   2040-05 [1],[3],[5]
Fair Value   1,319 [1],[3],[5]
Principal And Interest - Fixed Rate Agency Securities [Member] | Other Government National Mortgage Association Pool 5.50% 2041-03 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount   806 [1],[3],[5]
Description   Other Government National Mortgage Association Pool [1],[3],[5]
Rate   5.50% [1],[3],[5]
Maturity   2041-03 [1],[3],[5]
Fair Value   907 [1],[3],[5]
Principal And Interest - Fixed Rate Agency Securities [Member] | Federal National Mortgage Association Pool 4.00% 2026-06 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount 5,172 [1],[2],[4] 6,759 [1],[3],[5]
Description Federal National Mortgage Association Pool [1],[2],[4] Federal National Mortgage Association Pool [1],[3],[5]
Rate 4.00% [1],[2],[4] 4.00% [1],[3],[5]
Maturity 2026-06 [1],[2],[4] 2026-06 [1],[3],[5]
Fair Value 5,536 [1],[2],[4] 7,147 [1],[3],[5]
Principal And Interest - Fixed Rate Agency Securities [Member] | Federal Home Loan Mortgage Corporation Pool 6.00% 2039-04 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount 4,284 [1],[2],[4] 5,531 [1],[3],[5]
Description Federal Home Loan Mortgage Corporation Pool [1],[2],[4] Federal Home Loan Mortgage Corporation Pool [1],[3],[5]
Rate 6.00% [1],[2],[4] 6.00% [1],[3],[5]
Maturity 2039-04 [1],[2],[4] 2039-04 [1],[3],[5]
Fair Value 4,722 [1],[2],[4] 6,095 [1],[3],[5]
Principal And Interest - Fixed Rate Agency Securities [Member] | Federal National Mortgage Association Pool 5.00% 2040-11 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount 5,069 [1],[2],[4] 5,514 [1],[3],[5]
Description Federal National Mortgage Association Pool [1],[2],[4] Federal National Mortgage Association Pool [1],[3],[5]
Rate 5.00% [1],[2],[4] 5.00% [1],[3],[5]
Maturity 2040-11 [1],[2],[4] 2040-11 [1],[3],[5]
Fair Value 5,561 [1],[2],[4] 5,985 [1],[3],[5]
Principal And Interest - Fixed Rate Agency Securities [Member] | Federal National Mortgage Association Pool 4.50% 2041-08 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount 4,964 [1],[2],[4] 5,209 [1],[3],[5]
Description Federal National Mortgage Association Pool [1],[2],[4] Federal National Mortgage Association Pool [1],[3],[5]
Rate 4.50% [1],[2],[4] 4.50% [1],[3],[5]
Maturity 2041-08 [1],[2],[4] 2041-08 [1],[3],[5]
Fair Value 5,392 [1],[2],[4] 5,557 [1],[3],[5]
Principal And Interest - Fixed Rate Agency Securities [Member] | Federal National Mortgage Association Pool 5.00% 2040-06 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount 3,744 [1],[2],[4] 4,799 [1],[3],[5]
Description Federal National Mortgage Association Pool [1],[2],[4] Federal National Mortgage Association Pool [1],[3],[5]
Rate 5.00% [1],[2],[4] 5.00% [1],[3],[5]
Maturity 2040-06 [1],[2],[4] 2040-06 [1],[3],[5]
Fair Value 4,108 [1],[2],[4] 5,209 [1],[3],[5]
Principal And Interest - Fixed Rate Agency Securities [Member] | Federal Home Loan Mortgage Corporation Pool 4.50% 2041-09 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount 3,672 [1],[2],[4] 3,724 [1],[3],[5]
Description Federal Home Loan Mortgage Corporation Pool [1],[2],[4] Federal Home Loan Mortgage Corporation Pool [1],[3],[5]
Rate 4.50% [1],[2],[4] 4.50% [1],[3],[5]
Maturity 2041-09 [1],[2],[4] 2041-09 [1],[3],[5]
Fair Value 3,996 [1],[2],[4] 3,963 [1],[3],[5]
Principal And Interest - Fixed Rate Agency Securities [Member] | Other Federal National Mortgage Association Pools [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount 24,668 [1],[2],[4] 4,609 [1],[3],[5]
Description Other Federal National Mortgage Association Pools [1],[2],[4] Other Federal National Mortgage Association Pools [1],[3],[5]
Rate   6.00% [1],[3],[5]
Fair Value 26,867 [1],[2],[4] 5,092 [1],[3],[5]
Principal And Interest - Fixed Rate Agency Securities [Member] | Other Federal National Mortgage Association Pools [Member] | Maximum [Member]
    
Schedule of Investments [Line Items]    
Rate 6.00% [1],[2],[4]  
Maturity 2042-09 [1],[2],[4] 2040-02 [1],[3],[5]
Principal And Interest - Fixed Rate Agency Securities [Member] | Other Federal National Mortgage Association Pools [Member] | Minimum [Member]
    
Schedule of Investments [Line Items]    
Rate 3.50% [1],[2],[4]  
Maturity 2027-08 [1],[2],[4] 2039-09 [1],[3],[5]
Principal And Interest - Fixed Rate Agency Securities [Member] | Other Federal Home Loan Mortgage Corporation Pools [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount 7,268 [1],[2],[4]  
Description Other Federal Home Loan Mortgage Corporation Pools [1],[2],[4]  
Fair Value 7,858 [1],[2],[4]  
Principal And Interest - Fixed Rate Agency Securities [Member] | Other Federal Home Loan Mortgage Corporation Pools [Member] | Maximum [Member]
    
Schedule of Investments [Line Items]    
Rate 6.00% [1],[2],[4]  
Maturity 2042-09 [1],[2],[4]  
Principal And Interest - Fixed Rate Agency Securities [Member] | Other Federal Home Loan Mortgage Corporation Pools [Member] | Minimum [Member]
    
Schedule of Investments [Line Items]    
Rate 3.00% [1],[2],[4]  
Maturity 2027-09 [1],[2],[4]  
Interest Only - Fixed Rate Agency Securities [Member]
    
Schedule of Investments [Line Items]    
Investments owned as a percentage of net assets 0.74% [1],[2],[4] 1.38% [1],[3],[5]
Fair Value 3,661 [1],[2],[4] 5,109 [1],[3],[5]
Interest Only - Fixed Rate Agency Securities [Member] | Other Government National Mortgage Association 5.50% 2036-03 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount 5,669 [1],[2],[4] 9,281 [1],[3],[5]
Description Other Government National Mortgage Association [1],[2],[4] Other Government National Mortgage Association [1],[3],[5]
Rate 5.50% [1],[2],[4] 5.50% [1],[3],[5]
Maturity 2036-03 [1],[2],[4] 2036-03 [1],[3],[5]
Fair Value 282 [1],[2],[4] 603 [1],[3],[5]
Interest Only - Fixed Rate Agency Securities [Member] | Other Federal Home Loan Mortgage Corporation [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount 11,358 [1],[2],[4] 13,937 [1],[3],[5]
Description Other Federal Home Loan Mortgage Corporation [1],[2],[4] Other Federal Home Loan Mortgage Corporation [1],[3],[5]
Fair Value 1,214 [1],[2],[4] 1,772 [1],[3],[5]
Interest Only - Fixed Rate Agency Securities [Member] | Other Federal Home Loan Mortgage Corporation [Member] | Maximum [Member]
    
Schedule of Investments [Line Items]    
Rate 5.50% [1],[2],[4] 5.50% [1],[3],[5]
Maturity 2039-01 [1],[2],[4] 2039-01 [1],[3],[5]
Interest Only - Fixed Rate Agency Securities [Member] | Other Federal Home Loan Mortgage Corporation [Member] | Minimum [Member]
    
Schedule of Investments [Line Items]    
Rate 5.00% [1],[2],[4] 5.00% [1],[3],[5]
Maturity 2033-06 [1],[2],[4] 2033-06 [1],[3],[5]
Interest Only - Fixed Rate Agency Securities [Member] | Other Federal National Mortgage Association [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount 23,569 [1],[2],[4] 24,381 [1],[3],[5]
Description Other Federal National Mortgage Association [1],[2],[4] Other Federal National Mortgage Association [1],[3],[5]
Fair Value 2,165 [1],[2],[4] 2,734 [1],[3],[5]
Interest Only - Fixed Rate Agency Securities [Member] | Other Federal National Mortgage Association [Member] | Maximum [Member]
    
Schedule of Investments [Line Items]    
Rate 5.50% [1],[2],[4] 5.50% [1],[3],[5]
Maturity 2040-10 [1],[2],[4] 2040-10 [1],[3],[5]
Interest Only - Fixed Rate Agency Securities [Member] | Other Federal National Mortgage Association [Member] | Minimum [Member]
    
Schedule of Investments [Line Items]    
Rate 4.00% [1],[2],[4] 5.00% [1],[3],[5]
Maturity 2036-01 [1],[2],[4] 2036-01 [1],[3],[5]
TBA - Fixed Rate Agency Securities [Member]
    
Schedule of Investments [Line Items]    
Investments owned as a percentage of net assets 6.76% [1],[2],[4] 8.64% [1],[3],[5]
Fair Value 33,723 [1],[2],[4] 32,033 [1],[3],[5]
TBA - Fixed Rate Agency Securities [Member] | Federal Home Loan Mortgage Corporation (30 Year) 4.00% 2012-10 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount 21,550 [1],[2],[4]  
Description Federal Home Loan Mortgage Corporation (30 Year) [1],[2],[4]  
Rate 4.00% [1],[2],[4]  
Maturity 2012-10 [1],[2],[4]  
Fair Value 23,168 [1],[2],[4]  
TBA - Fixed Rate Agency Securities [Member] | Federal National Mortgage Association (30 Year) 3.00% 2012-10 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount 10,000 [1],[2],[4]  
Description Federal National Mortgage Association (30 Year) [1],[2],[4]  
Rate 3.00% [1],[2],[4]  
Maturity 2012-10 [1],[2],[4]  
Fair Value 10,555 [1],[2],[4]  
TBA - Fixed Rate Agency Securities [Member] | Federal National Mortgage Association (30 Year) 4.00% 2012-01 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount   30,500 [1],[3],[5]
Description   Federal National Mortgage Association (30 Year) [1],[3],[5]
Rate   4.00% [1],[3],[5]
Maturity   2012-01 [1],[3],[5]
Fair Value   32,033 [1],[3],[5]
Floating Rate Agency Securities [Member]
    
Schedule of Investments [Line Items]    
Investments owned as a percentage of net assets 4.13% [1],[2],[4] 10.29% [1],[3],[5]
Fair Value 20,583 [1],[2],[4] 38,184 [1],[3],[5]
Investments at value, cost 20,001 [1],[2],[4] 37,594 [1],[3],[5]
Principal And Interest - Floating Rate Agency Securities [Member]
    
Schedule of Investments [Line Items]    
Investments owned as a percentage of net assets 4.10% [1],[2],[4] 10.23% [1],[3],[5]
Fair Value 20,417 [1],[2],[4] 37,956 [1],[3],[5]
Principal And Interest - Floating Rate Agency Securities [Member] | Federal National Mortgage Association Pool 5.24% 2035-12 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount 5,358 [1],[2],[4]  
Description Federal National Mortgage Association Pool [1],[2],[4]  
Rate 5.24% [1],[2],[4]  
Maturity 2035-12 [1],[2],[4]  
Fair Value 5,650 [1],[2],[4]  
Principal And Interest - Floating Rate Agency Securities [Member] | Federal National Mortgage Association Pool 5.50% 2037-07 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount 2,712 [1],[2],[4]  
Description Federal National Mortgage Association Pool [1],[2],[4]  
Rate 5.50% [1],[2],[4]  
Maturity 2037-07 [1],[2],[4]  
Fair Value 2,912 [1],[2],[4]  
Principal And Interest - Floating Rate Agency Securities [Member] | Federal National Mortgage Association Pool 5.10% 2038-05 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount 7,115 [1],[2],[4] 9,464 [1],[3],[5]
Description Federal National Mortgage Association Pool [1],[2],[4] Federal National Mortgage Association Pool [1],[3],[5]
Rate 5.10% [1],[2],[4] 5.10% [1],[3],[5]
Maturity 2038-05 [1],[2],[4] 2038-05 [1],[3],[5]
Fair Value 7,501 [1],[2],[4] 9,969 [1],[3],[5]
Principal And Interest - Floating Rate Agency Securities [Member] | Federal National Mortgage Association Pool 5.28% 2035-12 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount   6,675 [1],[3],[5]
Description   Federal National Mortgage Association Pool [1],[3],[5]
Rate   5.28% [1],[3],[5]
Maturity   2035-12 [1],[3],[5]
Fair Value   7,027 [1],[3],[5]
Principal And Interest - Floating Rate Agency Securities [Member] | Federal National Mortgage Association Pool 5.29% 2038-02 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount   6,627 [1],[3],[5]
Description   Federal National Mortgage Association Pool [1],[3],[5]
Rate   5.29% [1],[3],[5]
Maturity   2038-02 [1],[3],[5]
Fair Value   6,954 [1],[3],[5]
Principal And Interest - Floating Rate Agency Securities [Member] | Federal Home Loan Mortgage Corporation Pool 2.71% 2034-07 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount   3,364 [1],[3],[5]
Description   Federal Home Loan Mortgage Corporation Pool [1],[3],[5]
Rate   2.71% [1],[3],[5]
Maturity   2034-07 [1],[3],[5]
Fair Value   3,524 [1],[3],[5]
Principal And Interest - Floating Rate Agency Securities [Member] | Federal National Mortgage Association Pool 5.52% 2037-07 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount   3,261 [1],[3],[5]
Description   Federal National Mortgage Association Pool [1],[3],[5]
Rate   5.52% [1],[3],[5]
Maturity   2037-07 [1],[3],[5]
Fair Value   3,493 [1],[3],[5]
Principal And Interest - Floating Rate Agency Securities [Member] | Federal National Mortgage Association Pool 5.44% 2037-09 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount   1,906 [1],[3],[5]
Description   Federal National Mortgage Association Pool [1],[3],[5]
Rate   5.44% [1],[3],[5]
Maturity   2037-09 [1],[3],[5]
Fair Value   2,023 [1],[3],[5]
Principal And Interest - Floating Rate Agency Securities [Member] | Other Federal National Mortgage Association Pool 5.01% 2033-10 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount   1,444 [1],[3],[5]
Description   Other Federal National Mortgage Association Pool [1],[3],[5]
Rate   5.01% [1],[3],[5]
Maturity   2033-10 [1],[3],[5]
Fair Value   1,525 [1],[3],[5]
Principal And Interest - Floating Rate Agency Securities [Member] | Federal National Mortgage Association Pool 5.69% 2036-04 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount 3,034 [1],[2],[4] 3,247 [1],[3],[5]
Description Federal National Mortgage Association Pool [1],[2],[4] Federal National Mortgage Association Pool [1],[3],[5]
Rate 5.69% [1],[2],[4] 5.69% [1],[3],[5]
Maturity 2036-04 [1],[2],[4] 2036-04 [1],[3],[5]
Fair Value 3,218 [1],[2],[4] 3,441 [1],[3],[5]
Principal And Interest - Floating Rate Agency Securities [Member] | Other Federal National Mortgage Association Pool 5.27% 2037-09 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount 1,066 [1],[2],[4]  
Description Other Federal National Mortgage Association Pool [1],[2],[4]  
Rate 5.27% [1],[2],[4]  
Maturity 2037-09 [1],[2],[4]  
Fair Value 1,136 [1],[2],[4]  
Interest Only - Floating Rate Agency Securities [Member]
    
Schedule of Investments [Line Items]    
Investments owned as a percentage of net assets 0.03% [1],[2],[4] 0.06% [1],[3],[5]
Fair Value 166 [1],[2],[4] 228 [1],[3],[5]
Interest Only - Floating Rate Agency Securities [Member] | Other Federal National Mortgage Association 5.50% 2036-08 [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount 1,155 [1],[2],[4] 1,476 [1],[3],[5]
Description Other Federal National Mortgage Association [1],[2],[4] Other Federal National Mortgage Association Pool [1],[3],[5]
Rate 5.50% [1],[2],[4] 5.50% [1],[3],[5]
Maturity 2036-08 [1],[2],[4] 2036-08 [1],[3],[5]
Fair Value 166 [1],[2],[4] 228 [1],[3],[5]
Private Label Securities [Member]
    
Schedule of Investments [Line Items]    
Investments owned as a percentage of net assets 101.70% [1],[2] 116.91% [1],[3]
Fair Value 507,121 [1],[2] 433,626 [1],[3]
Investments at value, cost 487,008 [1],[2] 463,652 [1],[3]
Principal And Interest - Private Label Securities [Member]
    
Schedule of Investments [Line Items]    
Investments owned as a percentage of net assets 101.02% [1],[2] 114.91% [1],[3]
Fair Value 503,745 [1],[2] 426,202 [1],[3]
Investments at value, cost 483,548 [1],[2] 456,170 [1],[3]
Principal And Interest - Private Label Securities [Member] | Various Issuer [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount 824,471 [1],[2] 762,480 [1],[3]
Description Various [1],[2] Various [1],[3]
Fair Value 503,745 [1],[2] 426,202 [1],[3]
Principal And Interest - Private Label Securities [Member] | Various Issuer [Member] | Maximum [Member]
    
Schedule of Investments [Line Items]    
Rate 9.35% [1],[2] 9.35% [1],[3]
Maturity 2051-02 [1],[2] 2047-12 [1],[3]
Principal And Interest - Private Label Securities [Member] | Various Issuer [Member] | Minimum [Member]
    
Schedule of Investments [Line Items]    
Rate 0.28% [1],[2] 0.35%
Maturity 2019-05 [1],[2] 2019-05 [1],[3]
Principal Only - Private Label Securities [Member]
    
Schedule of Investments [Line Items]    
Investments owned as a percentage of net assets 0.43% [1],[2]  
Fair Value 2,146 [1],[2]  
Investments at value, cost 2,189 [1],[2]  
Principal Only - Private Label Securities [Member] | Various Issuer [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount 5,800 [1],[2]  
Description Various [1],[2]  
Rate 0.00% [1],[2]  
Maturity 2030-08 [1],[2]  
Fair Value 2,146 [1],[2]  
Interest Only - Private Label Securities [Member]
    
Schedule of Investments [Line Items]    
Investments owned as a percentage of net assets 0.25% [1],[2] 0.48% [1],[3]
Fair Value 1,230 [1],[2] 1,774 [1],[3]
Investments at value, cost 796 [1],[2] 1,471 [1],[3]
Interest Only - Private Label Securities [Member] | Various Issuer [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount 65,872 [1],[2] 76,167 [1],[3]
Description Various [1],[2] Various [1],[3]
Fair Value 1,230 [1],[2] 1,774 [1],[3]
Interest Only - Private Label Securities [Member] | Various Issuer [Member] | Maximum [Member]
    
Schedule of Investments [Line Items]    
Rate 2.00% [1],[2] 6.91% [1],[3]
Maturity 2047-09 [1],[2] 2047-09 [1],[3]
Interest Only - Private Label Securities [Member] | Various Issuer [Member] | Minimum [Member]
    
Schedule of Investments [Line Items]    
Rate 0.50% [1],[2] 0.50% [1],[3]
Maturity 2044-06 [1],[2] 2035-07 [1],[3]
Other Private Label Securities [Member]
    
Schedule of Investments [Line Items]    
Investments owned as a percentage of net assets 0.00% [1],[2] 1.52% [1],[3]
Fair Value 0 [1],[2] 5,650 [1],[3]
Investments at value, cost 475 [1],[2] 6,011 [1],[3]
Other Private Label Securities [Member] | Various Issuer [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount 175,151 [1],[2] 201,831 [1],[3]
Description Various [1],[2] Various [1],[3]
Rate 0.00% [1],[2] 0.00% [1],[3]
Maturity 2037-06 [1],[2]  
Fair Value 0 [1],[2] 5,650 [1],[3]
Other Private Label Securities [Member] | Various Issuer [Member] | Maximum [Member]
    
Schedule of Investments [Line Items]    
Maturity   2046-09 [1],[3]
Other Private Label Securities [Member] | Various Issuer [Member] | Minimum [Member]
    
Schedule of Investments [Line Items]    
Maturity   2037-06 [1],[3]
Commercial Mortgage Loans [Member]
    
Schedule of Investments [Line Items]    
Investments owned as a percentage of net assets 0.93% [1],[2],[6] 1.19% [1],[3],[6]
Fair Value 4,650 [1],[2],[6] 4,400 [1],[3],[6]
Investments at value, cost 4,860 [1],[2],[6] 4,789 [1],[3],[6]
Commercial Mortgage Loans [Member] | Various Issuer [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount 5,000 [1],[2],[6] 5,000 [1],[3],[6]
Description Various [1],[2],[6] Various [1],[3],[6]
Rate 6.25% [1],[2],[6] 6.25% [1],[3],[6]
Maturity 2013-11 [1],[2],[6] 2012-11 [1],[3],[6]
Fair Value 4,650 [1],[2],[6] 4,400 [1],[3],[6]
U.S. Treasury Securities [Member]
    
Schedule of Investments [Line Items]    
Investments owned as a percentage of net assets   2.72% [1],[3]
Fair Value   10,113 [1],[3]
Investments at value, cost   9,991 [1],[3]
U.S. Treasury Securities [Member] | US Treasury Note [Member]
    
Schedule of Investments [Line Items]    
Current Principal/Notional Amount   10,000 [1],[3]
Description   U.S. Treasury Note [1],[3]
Rate   2.00% [1],[3]
Maturity   2021-11 [1],[3]
Fair Value   $ 10,113 [1],[3]
[1] See Note 2 and Note 3 in Notes to Consolidated Financial Statements.
[2] The table below shows the Company's long investment ratings from Moody's, Standard and Poor's, or Fitch, as well as the Company's long investments that were unrated but affiliated with Fannie Mae, Freddie Mac, or Ginnie Mae. Ratings tend to be a lagging credit indicator; as a result, the credit quality of the Company's long investment holdings may be lower than the credit quality implied based on the ratings listed below. In situations where an investment has a split rating, the lowest provided rating is used. The ratings descriptions include ratings qualified with a "+", "-", "1", "2", or "3". Percentage of Shareholders' Rating Description Equity Unrated but Agency-Guaranteed 131.13 % Aaa/AAA/AAA 0.02 % Aa/AA/AA 0.45 % A/A/A 1.85 % Baa/BBB/BBB 8.25 % Ba/BB/BB or below 90.44 % Unrated 1.62 %
[3] The table below shows the Company's long investment ratings from Moody's, Standard and Poor's, or Fitch, as well as the Company's long investments that were unrated but affiliated with Fannie Mae, Freddie Mac, or Ginnie Mae. Ratings tend to be a lagging credit indicator; as a result, the credit quality of the Company's long investment holdings may be lower than the credit quality implied based on the ratings listed below. In situations where an investment has a split rating, the lowest provided rating is used. The ratings descriptions include ratings qualified with a "+," "-," "1," "2" or "3." Percentage of Rating Description Shareholders' Equity U.S. Treasury Securities 2.72 % Unrated but Agency-Guaranteed 206.07 % Aaa/AAA/AAA 1.25 % Aa/AA/AA 1.88 % A/A/A 5.44 % Baa/BBB/BBB 3.46 % Ba/BB/BB or below 103.36 % Unrated 2.71 %
[4] At September 30, 2012, the Company's long investments guaranteed by the Federal National Mortgage Association, the Federal Home Loan Mortgage Corporation, and the Government National Mortgage Association represented 104.58%, 25.88%, and 0.67% of shareholders' equity, respectively.
[5] At December 31, 2011, the Company's long investments guaranteed by the Federal National Mortgage Association, the Federal Home Loan Mortgage Corporation, and the Government National Mortgage Association represented 142.04%, 63.62%, and 0.41% of shareholders' equity, respectively.
[6] Maturity date may be extended through November 4, 2015.