Mortgage Loans on Real Estate Schedule of Mortgage Loan Portfolio by Geographic Region and Property Type (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Receivable, Gross, Commercial, Real Estate	$ 2,600,000	$ 2,800,000
Commercial Real Estate Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Receivable, Gross, Commercial, Real Estate	2,658,883	2,856,011
Percent of Mortgage Loans	100.00%	100.00%
Commercial Real Estate Portfolio Segment [Member] \| Mortgage Loans Office Property Type [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Receivable, Gross, Commercial, Real Estate	666,467	777,343
Percent of Mortgage Loans	25.10%	27.20%
Commercial Real Estate Portfolio Segment [Member] \| Mortgage Loans Medical Office Property Type [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Receivable, Gross, Commercial, Real Estate	136,764	175,580
Percent of Mortgage Loans	5.10%	6.10%
Commercial Real Estate Portfolio Segment [Member] \| Mortgage Loans Retail Property Type [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Receivable, Gross, Commercial, Real Estate	677,951	635,916
Percent of Mortgage Loans	25.50%	22.30%
Commercial Real Estate Portfolio Segment [Member] \| Mortgage Loans Industrial and Warehouse Property Type [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Receivable, Gross, Commercial, Real Estate	692,637	710,426
Percent of Mortgage Loans	26.10%	24.90%
Commercial Real Estate Portfolio Segment [Member] \| Mortgage Loans Hotel Property Type [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Receivable, Gross, Commercial, Real Estate	94,045	139,193
Percent of Mortgage Loans	3.50%	4.90%
Commercial Real Estate Portfolio Segment [Member] \| Mortgage Loans Apartment Property Type [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Receivable, Gross, Commercial, Real Estate	219,335	187,548
Percent of Mortgage Loans	8.20%	6.60%
Commercial Real Estate Portfolio Segment [Member] \| Mortgage Loans Mixed Use or Other Property Type [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Receivable, Gross, Commercial, Real Estate	171,684	230,005
Percent of Mortgage Loans	6.50%	8.00%
Commercial Real Estate Portfolio Segment [Member] \| Mortgage Loans East United States Region [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Receivable, Gross, Commercial, Real Estate	732,762	719,231
Percent of Mortgage Loans	27.50%	25.20%
Commercial Real Estate Portfolio Segment [Member] \| Mortgage Loans Middle Atlantic United States Region [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Receivable, Gross, Commercial, Real Estate	155,094	169,240
Percent of Mortgage Loans	5.80%	5.90%
Commercial Real Estate Portfolio Segment [Member] \| Mortgage Loans Mountain United States Region [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Receivable, Gross, Commercial, Real Estate	387,599	411,054
Percent of Mortgage Loans	14.60%	14.40%
Commercial Real Estate Portfolio Segment [Member] \| Mortgage Loans New England United States Region [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Receivable, Gross, Commercial, Real Estate	26,385	36,815
Percent of Mortgage Loans	1.00%	1.30%
Commercial Real Estate Portfolio Segment [Member] \| Mortgage Loans Pacific United States Region [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Receivable, Gross, Commercial, Real Estate	320,982	309,693
Percent of Mortgage Loans	12.10%	10.80%
Commercial Real Estate Portfolio Segment [Member] \| Mortgage Loans South Atlantic United States Region [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Receivable, Gross, Commercial, Real Estate	458,802	493,764
Percent of Mortgage Loans	17.30%	17.30%
Commercial Real Estate Portfolio Segment [Member] \| Mortgage Loans West North Central United States Region [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Receivable, Gross, Commercial, Real Estate	370,168	487,693
Percent of Mortgage Loans	13.90%	17.10%
Commercial Real Estate Portfolio Segment [Member] \| Mortgage Loans West South Central United States Region [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Receivable, Gross, Commercial, Real Estate	$ 207,091	$ 228,521
Percent of Mortgage Loans	7.80%	8.00%

Amount before allowance of commercial loans issued to businesses to acquire, develop, construct, improve, or refinance land or building. Includes deferred interest and fees, undisbursed portion of loan balance, unamortized costs and premiums and discounts from face amounts. Excludes loans covered under loss sharing agreements.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 7

-Subparagraph a

-Article 9

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-03.7(a))

-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 3

-URI http://asc.fasb.org/extlink&oid=7512638&loc=d3e5066-111524

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.7-03.1(c))

-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher AICPA

-Name Statement of Position (SOP)

-Number 01-6

-Paragraph 13

-Subparagraph e

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 6: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 60

-Paragraph 47

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 7: http://www.xbrl.org/2003/role/presentationRef

-Publisher AICPA

-Name Audit and Accounting Guide (AAG)

-Number AAG-DEP

-Paragraph 51, 52, 53

-IssueDate 2006-05-01

-Chapter 8

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

+ Details