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Securities (Tables) | 9 Months Ended
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Sep. 30, 2018
Marketable Securities [Abstract] |
Trading Securities, [Table Text Block] | The fair value and net unrealized gain (loss) included in trading securities are as follows (in thousands):
|  | September 30, 2018 |  | December 31, 2017 |  | September 30, 2017
|  | Fair Value |  | Net Unrealized Gain (Loss) |  | Fair Value |  | Net Unrealized Gain (Loss) |  | Fair Value |  | Net Unrealized Gain (Loss)
U.S. government agency debentures |  | $ | 80,692 |  |  | $ | 21 |  |  | $ | 21,196 |  |  | $ | 8 |  |  | $ | 30,162 |  |  | $ | (101 | )
U.S. government agency residential mortgage-backed securities |  | 1,378,450 |  |  | (3,498 | ) |  | 392,673 |  |  | (517 | ) |  | 516,760 |  |  | 723 |
Municipal and other tax-exempt securities |  | 41,345 |  |  | (161 | ) |  | 13,559 |  |  | 83 |  |  | 56,148 |  |  | 153 |
Asset-backed securities |  | 72,309 |  |  | (100 | ) |  | 23,885 |  |  | (26 | ) |  | — |  |  | — |
Other trading securities |  | 40,604 |  |  | 5 |  |  | 11,363 |  |  | 4 |  |  | 11,047 |  |  | 23 |
Total trading securities |  | $ | 1,613,400 |  |  | $ | (3,733 | ) |  | $ | 462,676 |  |  | $ | (448 | ) |  | $ | 614,117 |  |  | $ | 798 |
Investment Securities (Held-to-Maturity) [Table Text Block] | The amortized cost and fair values of investment securities are as follows (in thousands):
|  | September 30, 2018
|  | Amortized |  | Fair |  | Gross Unrealized
|  | Cost |  | Value |  | Gain |  | Loss
Municipal and other tax-exempt |  | $ | 157,723 |  |  | $ | 158,230 |  |  | $ | 1,403 |  |  | $ | (896 | )
U.S. government agency residential mortgage-backed securities |  | 13,234 |  |  | 13,201 |  |  | 205 |  |  | (238 | )
Other debt securities |  | 203,082 |  |  | 211,462 |  |  | 10,721 |  |  | (2,341 | )
Total investment securities |  | $ | 374,039 |  |  | $ | 382,893 |  |  | $ | 12,329 |  |  | $ | (3,475 | )
|  | December 31, 2017
|  | Amortized |  | Fair |  | Gross Unrealized
|  | Cost |  | Value |  | Gain |  | Loss
Municipal and other tax-exempt |  | $ | 228,186 |  |  | $ | 230,349 |  |  | $ | 2,967 |  |  | $ | (804 | )
U.S. government agency residential mortgage-backed securities |  | 15,891 |  |  | 16,242 |  |  | 446 |  |  | (95 | )
Other debt securities |  | 217,716 |  |  | 233,444 |  |  | 17,095 |  |  | (1,367 | )
Total investment securities |  | $ | 461,793 |  |  | $ | 480,035 |  |  | $ | 20,508 |  |  | $ | (2,266 | )
|  | September 30, 2017
|  | Amortized |  | Fair |  | Gross Unrealized
|  | Cost |  | Value |  | Gain |  | Loss
Municipal and other tax-exempt |  | $ | 246,000 |  |  | $ | 249,250 |  |  | $ | 3,415 |  |  | $ | (165 | )
U.S. government agency residential mortgage-backed securities |  | 16,926 |  |  | 17,458 |  |  | 594 |  |  | (62 | )
Other debt securities |  | 203,636 |  |  | 223,187 |  |  | 20,141 |  |  | (590 | )
Total investment securities |  | $ | 466,562 |  |  | $ | 489,895 |  |  | $ | 24,150 |  |  | $ | (817 | )
The amortized cost and fair values of investment securities at September 30, 2018, by contractual maturity, are as shown in the following table (dollars in thousands):
|  | Less than One Year |  | One to Five Years |  | Six to Ten Years |  | Over Ten Years |  | Total |  | Weighted Average Maturity²
Municipal and other tax-exempt: |  |  |  |  |  |  |  |  |  |  |  |
Amortized cost |  | $ | 65,789 |  |  | $ | 41,827 |  |  | $ | 35,652 |  |  | $ | 14,455 |  |  | $ | 157,723 |  |  | 4.13 |
Fair value |  | 65,633 |  |  | 41,432 |  |  | 36,677 |  |  | 14,488 |  |  | 158,230 |  |  |
Nominal yield¹ |  | 2.06 | % |  | 2.82 | % |  | 6.00 | % |  | 4.33 | % |  | 3.36 | % |  |
Other debt securities: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Amortized cost |  | 14,847 |  |  | 60,825 |  |  | 115,587 |  |  | 11,823 |  |  | 203,082 |  |  | 7.23 |
Fair value |  | 14,941 |  |  | 62,604 |  |  | 123,236 |  |  | 10,681 |  |  | 211,462 |  |  |
Nominal yield |  | 4.17 | % |  | 4.70 | % |  | 5.76 | % |  | 4.34 | % |  | 5.25 | % |  |
Total fixed maturity securities: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Amortized cost |  | $ | 80,636 |  |  | $ | 102,652 |  |  | $ | 151,239 |  |  | $ | 26,278 |  |  | $ | 360,805 |  |  | 5.88 |
Fair value |  | 80,574 |  |  | 104,036 |  |  | 159,913 |  |  | 25,169 |  |  | 369,692 |  |  |  |
Nominal yield |  | 2.44 | % |  | 3.94 | % |  | 5.82 | % |  | 4.33 | % |  | 4.42 | % |  |  |
Residential mortgage-backed securities: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Amortized cost |  |  |  |  |  |  |  |  |  |  |  |  |  | $ | 13,234 |  |  | ³ |
Fair value |  |  |  |  |  |  |  |  |  |  |  |  |  | 13,201 |  |  |  |
Nominal yield4 |  |  |  |  |  |  |  |  |  |  |  |  |  | 2.77 | % |  |  |
Total investment securities: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Amortized cost |  |  |  |  |  |  |  |  |  |  |  |  |  | $ | 374,039 |  |  |  |
Fair value |  |  |  |  |  |  |  |  |  |  |  |  |  | 382,893 |  |  |  |
Nominal yield |  |  |  |  |  |  |  |  |  |  |  |  |  | 4.36 | % |  |  |
1 | Calculated on a taxable equivalent basis using a 25 percent effective tax rate.
2 | Expected maturities may differ from contractual maturities, because borrowers may have the right to call or prepay obligations with or without penalty.
3 | The average expected lives of residential mortgage-backed securities were 5.2 years based upon current prepayment assumptions.
4 The nominal yield on residential mortgage-backed securities is based upon prepayment assumptions at the purchase date. Actual yields earned may differ significantly based upon actual prepayments. See Quarterly Financial Summary - Unaudited for current yields on the investment securities portfolio.
Available For Sale Securities [Table Text Block] | The amortized cost and fair value of available for sale securities are as follows (in thousands):
|  | September 30, 2018
|  | Amortized |  | Fair |  | Gross Unrealized |  |
|  | Cost |  | Value |  | Gain |  | Loss |  | OTTI
U.S. Treasury |  | $ | 495 |  |  | $ | 490 |  |  | $ | — |  |  | $ | (5 | ) |  | $ | — |
Municipal and other tax-exempt |  | 4,269 |  |  | 4,349 |  |  | 81 |  |  | (1 | ) |  | — |
Residential mortgage-backed securities: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
U. S. government agencies: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
FNMA |  | 3,057,570 |  |  | 2,959,457 |  |  | 1,653 |  |  | (99,766 | ) |  | — |
FHLMC |  | 1,562,569 |  |  | 1,512,928 |  |  | 501 |  |  | (50,142 | ) |  | — |
GNMA |  | 677,496 |  |  | 659,967 |  |  | 450 |  |  | (17,979 | ) |  | — |
Total U.S. government agencies |  | 5,297,635 |  |  | 5,132,352 |  |  | 2,604 |  |  | (167,887 | ) |  | — |
Private issue |  | 54,932 |  |  | 74,685 |  |  | 19,753 |  |  | — |  |  | — |
Total residential mortgage-backed securities |  | 5,352,567 |  |  | 5,207,037 |  |  | 22,357 |  |  | (167,887 | ) |  | — |
Commercial mortgage-backed securities guaranteed by U.S. government agencies |  | 2,905,974 |  |  | 2,834,691 |  |  | 1,363 |  |  | (72,646 | ) |  | — |
Other debt securities |  | 25,502 |  |  | 25,447 |  |  | 11 |  |  | (66 | ) |  | — |
Total available for sale securities |  | $ | 8,288,807 |  |  | $ | 8,072,014 |  |  | $ | 23,812 |  |  | $ | (240,605 | ) |  | $ | — |
|  | December 31, 2017
|  | Amortized |  | Fair |  | Gross Unrealized |  |
|  | Cost |  | Value |  | Gain |  | Loss |  | OTTI
U.S. Treasury |  | $ | 1,000 |  |  | $ | 1,000 |  |  | $ | — |  |  | $ | — |  |  | $ | — |
Municipal and other tax-exempt |  | 27,182 |  |  | 27,080 |  |  | 181 |  |  | (283 | ) |  | — |
Residential mortgage-backed securities: |  |  |  |  |  |  |  |  |  |  |  |  |  |
U. S. government agencies: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
FNMA |  | 3,021,551 |  |  | 2,997,563 |  |  | 11,549 |  |  | (35,537 | ) |  | — |
FHLMC |  | 1,545,971 |  |  | 1,531,009 |  |  | 3,148 |  |  | (18,110 | ) |  | — |
GNMA |  | 787,626 |  |  | 780,580 |  |  | 1,607 |  |  | (8,653 | ) |  | — |
Total U.S. government agencies |  | 5,355,148 |  |  | 5,309,152 |  |  | 16,304 |  |  | (62,300 | ) |  | — |
Private issue |  | 74,311 |  |  | 93,221 |  |  | 19,301 |  |  | — |  |  | (391 | )
Total residential mortgage-backed securities |  | 5,429,459 |  |  | 5,402,373 |  |  | 35,605 |  |  | (62,300 | ) |  | (391 | )
Commercial mortgage-backed securities guaranteed by U.S. government agencies |  | 2,858,885 |  |  | 2,834,961 |  |  | 1,963 |  |  | (25,887 | ) |  | — |
Other debt securities |  | 25,500 |  |  | 25,481 |  |  | 50 |  |  | (69 | ) |  | — |
Perpetual preferred stock |  | 12,562 |  |  | 15,767 |  |  | 3,205 |  |  | — |  |  | — |
Equity securities and mutual funds |  | 14,487 |  |  | 14,916 |  |  | 515 |  |  | (86 | ) |  | — |
Total available for sale securities |  | $ | 8,369,075 |  |  | $ | 8,321,578 |  |  | $ | 41,519 |  |  | $ | (88,625 | ) |  | $ | (391 | )
|  | September 30, 2017
|  | Amortized |  | Fair |  | Gross Unrealized |  |
|  | Cost |  | Value |  | Gain |  | Loss |  | OTTI
U.S. Treasury |  | $ | 1,000 |  |  | $ | 999 |  |  | $ | — |  |  | $ | (1 | ) |  | $ | — |
Municipal and other tax-exempt |  | 28,411 |  |  | 28,368 |  |  | 240 |  |  | (283 | ) |  | — |
Residential mortgage-backed securities: |  |  |  |  |  |  |  |  |  |
U. S. government agencies: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
FNMA |  | 3,103,869 |  |  | 3,108,822 |  |  | 25,510 |  |  | (20,557 | ) |  | — |
FHLMC |  | 1,331,212 |  |  | 1,330,159 |  |  | 6,630 |  |  | (7,683 | ) |  | — |
GNMA |  | 864,256 |  |  | 862,394 |  |  | 3,254 |  |  | (5,116 | ) |  | — |
Other |  | 25,000 |  |  | 25,009 |  |  | 51 |  |  | (42 | ) |  | — |
Total U.S. government agencies |  | 5,324,337 |  |  | 5,326,384 |  |  | 35,445 |  |  | (33,398 | ) |  | — |
Private issue |  | 80,797 |  |  | 99,994 |  |  | 19,197 |  |  | — |  |  | — |
Total residential mortgage-backed securities |  | 5,405,134 |  |  | 5,426,378 |  |  | 54,642 |  |  | (33,398 | ) |  | — |
Commercial mortgage-backed securities guaranteed by U.S. government agencies |  | 2,899,828 |  |  | 2,889,346 |  |  | 5,577 |  |  | (16,059 | ) |  | — |
Other debt securities |  | 4,400 |  |  | 4,153 |  |  | — |  |  | (247 | ) |  | — |
Perpetual preferred stock |  | 12,562 |  |  | 16,245 |  |  | 3,683 |  |  | — |  |  | — |
Equity securities and mutual funds |  | 17,803 |  |  | 17,710 |  |  | 655 |  |  | (748 | ) |  | — |
Total available for sale securities |  | $ | 8,369,138 |  |  | $ | 8,383,199 |  |  | $ | 64,797 |  |  | $ | (50,736 | ) |  | $ | — |
The amortized cost and fair values of available for sale securities at September 30, 2018, by contractual maturity, are as shown in the following table (dollars in thousands):
| Less than One Year |  | One to Five Years |  | Six to Ten Years |  | Over Ten Years |  | Total |  | Weighted Average Maturity4
U.S. Treasuries: |  |  |  |  |  |  |  |  |  |  |
Amortized cost | $ | — |  |  | $ | 495 |  |  | $ | — |  |  | $ | — |  |  | $ | 495 |  |  | 1.34 |
Fair value | — |  |  | 490 |  |  | — |  |  | — |  |  | 490 |  |  |
Nominal yield | — | % |  | 1.99 | % |  | — | % |  | — | % |  | 1.99 | % |  |
Municipal and other tax-exempt: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Amortized cost | $ | — |  |  | $ | — |  |  | $ | — |  |  | $ | 4,269 |  |  | $ | 4,269 |  |  | 18.72 |
Fair value | — |  |  | — |  |  | — |  |  | 4,349 |  |  | 4,349 |  |  |
Nominal yield¹ | — | % |  | — | % |  | — | % |  | 5.60 | % | 5 | 5.60 | % |  |
Commercial mortgage-backed securities: |  |  |  |  |  |  |  |  |  |  |
Amortized cost | $ | 74,694 |  |  | $ | 1,070,820 |  |  | $ | 1,449,084 |  |  | $ | 311,376 |  |  | $ | 2,905,974 |  |  | 7.11 |
Fair value | 73,929 |  |  | 1,043,429 |  |  | 1,413,692 |  |  | 303,641 |  |  | 2,834,691 |  |  |
Nominal yield | 1.70 | % |  | 2.02 | % |  | 2.24 | % |  | 2.45 | % |  | 2.17 | % |  |
Other debt securities: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Amortized cost | $ | — |  |  | $ | — |  |  | $ | — |  |  | $ | 25,502 |  |  | $ | 25,502 |  |  | 13.93 |
Fair value | — |  |  | — |  |  | — |  |  | 25,447 |  |  | 25,447 |  |  |
Nominal yield | — | % |  | — | % |  | — | % |  | 1.59 | % | 5 | 1.59 | % |  |
Total fixed maturity securities: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Amortized cost | $ | 74,694 |  |  | $ | 1,071,315 |  |  | $ | 1,449,084 |  |  | $ | 341,147 |  |  | $ | 2,936,240 |  |  | 7.18 |
Fair value | 73,929 |  |  | 1,043,919 |  |  | 1,413,692 |  |  | 333,437 |  |  | 2,864,977 |  |  |
Nominal yield | 1.70 | % |  | 2.02 | % |  | 2.24 | % |  | 2.42 | % |  | 2.17 | % |  |
Residential mortgage-backed securities: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Amortized cost |  |  |  |  |  |  |  |  |  |  |  |  | $ | 5,352,567 |  |  | 2 |
Fair value |  |  |  |  |  |  |  |  |  |  |  |  | 5,207,037 |  |  |
Nominal yield3 |  |  |  |  |  |  |  |  |  |  |  |  | 2.24 | % |  |
Total available-for-sale securities: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Amortized cost |  |  |  |  |  |  |  |  |  |  |  |  | $ | 8,288,807 |  |  |  |
Fair value |  |  |  |  |  |  |  |  |  |  |  |  | 8,072,014 |  |  |  |
Nominal yield |  |  |  |  |  |  |  |  |  |  |  |  | 2.21 | % |  |  |
1 | Calculated on a taxable equivalent basis using a 25 percent effective tax rate.
2 | The average expected lives of mortgage-backed securities were 4.4 years based upon current prepayment assumptions.
3 | The nominal yield on mortgage-backed securities is based upon prepayment assumptions at the purchase date. Actual yields earned may differ significantly based upon actual prepayments. See Quarterly Financial Summary –– Unaudited following for current yields on available for sale securities portfolio.
4 | Expected maturities may differ from contractual maturities because borrowers may have the right to call or prepay obligations with or without penalty.
5 | Nominal yield on municipal and other tax-exempt securities and other debt securities with contractual maturity dates over ten years are based on variable rates which generally are reset within 35 days.
Sales of available for sale securities resulted in gains and losses as follows (in thousands):
| Three Months Ended September 30, |  | Nine Months Ended September 30,
| 2018 |  | 2017 |  | 2018 |  | 2017
Proceeds | $ | 45,293 |  |  | $ | 265,632 |  |  | $ | 232,826 |  |  | $ | 966,044 |
Gross realized gains | 250 |  |  | 2,768 |  |  | 700 |  |  | 7,623 |
Gross realized losses | — |  |  | (281 | ) |  | (1,502 | ) |  | (2,707 | )
Related federal and state income tax expense (benefit) | 64 |  |  | 967 |  |  | (204 | ) |  | 1,912 |
Schedule of Unrealized Loss on Investments [Table Text Block] | Temporarily Impaired Securities as of September 30, 2018 (in thousands):
|  | Number of Securities |  | Less Than 12 Months |  | 12 Months or Longer |  | Total
|  |  | Fair Value |  | Unrealized Loss |  | Fair Value |  | Unrealized Loss |  | Fair Value |  | Unrealized Loss
Investment: |  |  |  |  |  |  |  |  |  |  |  |  |  |
Municipal and other tax-exempt |  | 85 |  |  | $ | 46,618 |  |  | $ | 277 |  |  | $ | 54,149 |  |  | $ | 619 |  |  | $ | 100,767 |  |  | $ | 896 |
U.S. government agency residential mortgage-backed securities |  | 3 |  |  | 6,682 |  |  | 96 |  |  | 2,625 |  |  | 142 |  |  | 9,307 |  |  | 238 |
Other debt securities |  | 93 |  |  | 38,441 |  |  | 2,035 |  |  | 4,714 |  |  | 306 |  |  | 43,155 |  |  | 2,341 |
Total investment securities |  | 181 |  |  | $ | 91,741 |  |  | $ | 2,408 |  |  | $ | 61,488 |  |  | $ | 1,067 |  |  | $ | 153,229 |  |  | $ | 3,475 |
|  | Number of Securities |  | Less Than 12 Months |  | 12 Months or Longer |  | Total
|  |  | Fair Value |  | Unrealized Loss |  | Fair Value |  | Unrealized Loss |  | Fair Value |  | Unrealized Loss
Available for sale: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
U.S. Treasury |  | 1 |  |  | $ | 490 |  |  | $ | 5 |  |  | $ | — |  |  | $ | — |  |  | $ | 490 |  |  | $ | 5 |
Municipal and other tax-exempt |  | 2 |  |  | 1,046 |  |  | 1 |  |  | — |  |  | — |  |  | 1,046 |  |  | 1 |
Residential mortgage-backed securities: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
U. S. government agencies: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
FNMA |  | 188 |  |  | 1,584,010 |  |  | 32,919 |  |  | 1,277,814 |  |  | 66,847 |  |  | 2,861,824 |  |  | 99,766 |
FHLMC |  | 99 |  |  | 702,707 |  |  | 15,450 |  |  | 781,589 |  |  | 34,692 |  |  | 1,484,296 |  |  | 50,142 |
GNMA |  | 38 |  |  | 285,731 |  |  | 5,326 |  |  | 253,506 |  |  | 12,653 |  |  | 539,237 |  |  | 17,979 |
Total U.S. government agencies |  | 325 |  |  | 2,572,448 |  |  | 53,695 |  |  | 2,312,909 |  |  | 114,192 |  |  | 4,885,357 |  |  | 167,887 |
Private issue1 |  | — |  |  | — |  |  | — |  |  | — |  |  | — |  |  | — |  |  | — |
Total residential mortgage-backed securities |  | 325 |  |  | 2,572,448 |  |  | 53,695 |  |  | 2,312,909 |  |  | 114,192 |  |  | 4,885,357 |  |  | 167,887 |
Commercial mortgage-backed securities guaranteed by U.S. government agencies |  | 220 |  |  | 1,174,544 |  |  | 24,982 |  |  | 1,238,848 |  |  | 47,664 |  |  | 2,413,392 |  |  | 72,646 |
Other debt securities |  | 2 |  |  | — |  |  | — |  |  | 20,435 |  |  | 66 |  |  | 20,435 |  |  | 66 |
Total available for sale securities |  | 550 |  |  | $ | 3,748,528 |  |  | $ | 78,683 |  |  | $ | 3,572,192 |  |  | $ | 161,922 |  |  | $ | 7,320,720 |  |  | $ | 240,605 |
1 | Includes securities for which an unrealized loss remains in AOCI after an other-than-temporary credit loss has been recognized in income.
Temporarily Impaired Securities as of December 31, 2017 (In thousands)
|  | Number of Securities |  | Less Than 12 Months |  | 12 Months or Longer |  | Total
|  |  | Fair Value |  | Unrealized Loss |  | Fair Value |  | Unrealized Loss |  | Fair Value |  | Unrealized Loss
Investment: |  |  |  |  |  |  |  |  |  |  |  |  |  |
Municipal and other tax-exempt |  | 100 |  |  | $ | 145,960 |  |  | $ | 643 |  |  | $ | 5,833 |  |  | $ | 161 |  |  | $ | 151,793 |  |  | $ | 804 |
U.S. government agency residential mortgage-backed securities |  | 1 |  |  | — |  |  | — |  |  | 3,356 |  |  | 95 |  |  | 3,356 |  |  | 95 |
Other debt securities |  | 49 |  |  | 20,091 |  |  | 1,238 |  |  | 3,076 |  |  | 129 |  |  | 23,167 |  |  | 1,367 |
Total investment securities |  | 150 |  |  | $ | 166,051 |  |  | $ | 1,881 |  |  | $ | 12,265 |  |  | $ | 385 |  |  | $ | 178,316 |  |  | $ | 2,266 |
|  | Number of Securities |  | Less Than 12 Months |  | 12 Months or Longer |  | Total
|  |  | Fair Value |  | Unrealized Loss |  | Fair Value |  | Unrealized Loss |  | Fair Value |  | Unrealized Loss
Available for sale: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
U.S. Treasury |  | — |  |  | $ | — |  |  | $ | — |  |  | $ | — |  |  | $ | — |  |  | $ | — |  |  | $ | — |
Municipal and other tax-exempt |  | 19 |  |  | 12,765 |  |  | 18 |  |  | 4,802 |  |  | 265 |  |  | 17,567 |  |  | 283 |
Residential mortgage-backed securities: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
U. S. government agencies: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
FNMA |  | 113 |  |  | 1,203,041 |  |  | 9,618 |  |  | 824,029 |  |  | 25,919 |  |  | 2,027,070 |  |  | 35,537 |
FHLMC |  | 69 |  |  | 863,778 |  |  | 7,297 |  |  | 385,816 |  |  | 10,813 |  |  | 1,249,594 |  |  | 18,110 |
GNMA |  | 27 |  |  | 201,887 |  |  | 1,452 |  |  | 248,742 |  |  | 7,201 |  |  | 450,629 |  |  | 8,653 |
Total U.S. government agencies |  | 209 |  |  | 2,268,706 |  |  | 18,367 |  |  | 1,458,587 |  |  | 43,933 |  |  | 3,727,293 |  |  | 62,300 |
Private issue1 |  | 8 |  |  | 5,898 |  |  | 391 |  |  | — |  |  | — |  |  | 5,898 |  |  | 391 |
Total residential mortgage-backed securities |  | 217 |  |  | 2,274,604 |  |  | 18,758 |  |  | 1,458,587 |  |  | 43,933 |  |  | 3,733,191 |  |  | 62,691 |
Commercial mortgage-backed securities guaranteed by U.S. government agencies |  | 185 |  |  | 1,465,703 |  |  | 11,824 |  |  | 652,296 |  |  | 14,063 |  |  | 2,117,999 |  |  | 25,887 |
Other debt securities |  | 2 |  |  | 19,959 |  |  | 41 |  |  | 472 |  |  | 28 |  |  | 20,431 |  |  | 69 |
Perpetual preferred stocks |  | — |  |  | — |  |  | — |  |  | — |  |  | — |  |  | — |  |  | — |
Equity securities and mutual funds |  | 111 |  |  | 911 |  |  | 7 |  |  | 2,203 |  |  | 79 |  |  | 3,114 |  |  | 86 |
Total available for sale securities |  | 534 |  |  | $ | 3,773,942 |  |  | $ | 30,648 |  |  | $ | 2,118,360 |  |  | $ | 58,368 |  |  | $ | 5,892,302 |  |  | $ | 89,016 |
1 | Includes securities for which an unrealized loss remains in AOCI after an other-than-temporary credit loss has been recognized in income.
Temporarily Impaired Securities as of September 30, 2017 (In thousands)
|  | Number of Securities |  | Less Than 12 Months |  | 12 Months or Longer |  | Total
|  |  | Fair Value |  | Unrealized Loss |  | Fair Value |  | Unrealized Loss |  | Fair Value |  | Unrealized Loss
Investment: |  |  |  |  |  |  |  |  |  |  |  |  |  |
Municipal and other tax-exempt |  | 63 |  |  | $ | 80,235 |  |  | $ | 70 |  |  | $ | 9,795 |  |  | $ | 95 |  |  | $ | 90,030 |  |  | $ | 165 |
U.S. government agency residential mortgage-backed securities |  | 1 |  |  | 3,578 |  |  | 62 |  |  | — |  |  | — |  |  | 3,578 |  |  | 62 |
Other debt securities |  | 28 |  |  | 10,022 |  |  | 566 |  |  | 427 |  |  | 24 |  |  | 10,449 |  |  | 590 |
Total investment securities |  | 92 |  |  | $ | 93,835 |  |  | $ | 698 |  |  | $ | 10,222 |  |  | $ | 119 |  |  | $ | 104,057 |  |  | $ | 817 |
|  | Number of Securities |  | Less Than 12 Months |  | 12 Months or Longer |  | Total
|  |  | Fair Value |  | Unrealized Loss |  | Fair Value |  | Unrealized Loss |  | Fair Value |  | Unrealized Loss
Available for sale: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
U.S. Treasury |  | 1 |  |  | $ | 999 |  |  | $ | 1 |  |  | $ | — |  |  | $ | — |  |  | $ | 999 |  |  | $ | 1 |
Municipal and other tax-exempt |  | 11 |  |  | 576 |  |  | 1 |  |  | 4,785 |  |  | 282 |  |  | 5,361 |  |  | 283 |
Residential mortgage-backed securities: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
U. S. government agencies: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
FNMA |  | 81 |  |  | 1,054,171 |  |  | 10,288 |  |  | 480,994 |  |  | 10,269 |  |  | 1,535,165 |  |  | 20,557 |
FHLMC |  | 42 |  |  | 477,823 |  |  | 3,546 |  |  | 198,478 |  |  | 4,137 |  |  | 676,301 |  |  | 7,683 |
GNMA |  | 17 |  |  | 166,565 |  |  | 1,718 |  |  | 124,037 |  |  | 3,398 |  |  | 290,602 |  |  | 5,116 |
Other |  | 1 |  |  | 19,958 |  |  | 42 |  |  | — |  |  | — |  |  | 19,958 |  |  | 42 |
Total U.S. government agencies |  | 141 |  |  | 1,718,517 |  |  | 15,594 |  |  | 803,509 |  |  | 17,804 |  |  | 2,522,026 |  |  | 33,398 |
Private issue1 |  | — |  |  | — |  |  | — |  |  | — |  |  | — |  |  | — |  |  | — |
Total residential mortgage-backed securities |  | 141 |  |  | 1,718,517 |  |  | 15,594 |  |  | 803,509 |  |  | 17,804 |  |  | 2,522,026 |  |  | 33,398 |
Commercial mortgage-backed securities guaranteed by U.S. government agencies |  | 137 |  |  | 1,154,911 |  |  | 7,194 |  |  | 559,984 |  |  | 8,865 |  |  | 1,714,895 |  |  | 16,059 |
Other debt securities |  | 2 |  |  | — |  |  | — |  |  | 4,153 |  |  | 247 |  |  | 4,153 |  |  | 247 |
Perpetual preferred stocks |  | — |  |  | — |  |  | — |  |  | — |  |  | — |  |  | — |  |  | — |
Equity securities and mutual funds |  | 91 |  |  | 3,672 |  |  | 696 |  |  | 1,428 |  |  | 52 |  |  | 5,100 |  |  | 748 |
Total available for sale securities |  | 383 |  |  | $ | 2,878,675 |  |  | $ | 23,486 |  |  | $ | 1,373,859 |  |  | $ | 27,250 |  |  | $ | 4,252,534 |  |  | $ | 50,736 |
1 | Includes securities for which an unrealized loss remains in AOCI after an other-than-temporary credit loss has been recognized in income.
Fair Value Option Securities [Table Text Block] | The fair value and net unrealized gain (loss) included in fair value option securities is as follows (in thousands):
|  | September 30, 2018 |  | December 31, 2017 |  | September 30, 2017
|  | Fair Value |  | Net Unrealized Gain (Loss) |  | Fair Value |  | Net Unrealized Gain (Loss) |  | Fair Value |  | Net Unrealized Gain (Loss)
U.S. government agency residential mortgage-backed securities |  | $ | 452,150 |  |  | $ | (7,923 | ) |  | $ | 755,054 |  |  | $ | (1,877 | ) |  | $ | 819,531 |  |  | $ | 1,671 |

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