Fair Value of Assets and Liabilities (Financial Instruments where Carrying Amounts and Fair Values May Differ) (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012		Dec. 31, 2011
Assets:
Policy loans	$ 13,880		$ 14,316
Accrued investment income	51,151		59,033
Liabilities:
Cash collateral for loaned securities	42,872		125,884
Short-term debt	73,918		27,803
Long-term debt	600,000		600,000
Carrying (Reported) Amount, Fair Value Disclosure [Member]
Assets:
Commercial mortgage and other loans	463,388	[1]	449,359
Policy loans	13,880	[1]	14,316
Cash	1,497	[1]	749
Accrued investment income	51,151	[1]	59,033
Other assets	48,510	[1]	12,237
Total Assets Financial Instruments Not Carried At Fair Value	578,426	[1]	535,694
Liabilities:
Investment contracts- policyholders' account balances	69,683	[1]	66,176
Cash collateral for loaned securities	42,872	[1]	125,884
Short-term debt	73,918	[1]	27,803
Long-term debt	600,000	[1]	600,000
Other liabilities	110,302	[1]	169,139
Separate account liabilities - investment contracts	1,082	[1]	1,192
Total Financial Instrument Liabilities Not Carried At Fair Value	897,857	[1]	990,194
Estimate of Fair Value, Fair Value Disclosure [Member]
Assets:
Commercial mortgage and other loans	507,859		490,151
Policy loans	13,880		14,316
Cash	1,497		749
Accrued investment income	51,151		59,033
Other assets	48,510		12,237
Total Assets Financial Instruments Not Carried At Fair Value	622,897		576,486
Liabilities:
Investment contracts- policyholders' account balances	70,824		66,659
Cash collateral for loaned securities	42,872		125,884
Short-term debt	73,918		27,803
Long-term debt	635,651		627,415
Other liabilities	110,302		169,139
Separate account liabilities - investment contracts	1,082		1,192
Total Financial Instrument Liabilities Not Carried At Fair Value	934,649		1,018,092
Estimate of Fair Value, Fair Value Disclosure [Member] | Fair Value, Inputs, Level 1 [Member]
Assets:
Commercial mortgage and other loans	0
Policy loans	0
Cash	1,497
Accrued investment income	0
Other assets	0
Total Assets Financial Instruments Not Carried At Fair Value	1,497
Liabilities:
Investment contracts- policyholders' account balances	0
Cash collateral for loaned securities	0
Short-term debt	0
Long-term debt	0
Other liabilities	0
Separate account liabilities - investment contracts	0
Total Financial Instrument Liabilities Not Carried At Fair Value	0
Estimate of Fair Value, Fair Value Disclosure [Member] | Fair Value, Inputs, Level 2 [Member]
Assets:
Commercial mortgage and other loans	0
Policy loans	0
Cash	0
Accrued investment income	51,151
Other assets	48,510
Total Assets Financial Instruments Not Carried At Fair Value	99,661
Liabilities:
Investment contracts- policyholders' account balances	0
Cash collateral for loaned securities	42,872
Short-term debt	73,918
Long-term debt	635,651
Other liabilities	110,302
Separate account liabilities - investment contracts	1,082
Total Financial Instrument Liabilities Not Carried At Fair Value	863,825
Estimate of Fair Value, Fair Value Disclosure [Member] | Fair Value, Inputs, Level 3 [Member]
Assets:
Commercial mortgage and other loans	507,859
Policy loans	13,880
Cash	0
Accrued investment income	0
Other assets	0
Total Assets Financial Instruments Not Carried At Fair Value	521,739
Liabilities:
Investment contracts- policyholders' account balances	70,824
Cash collateral for loaned securities	0
Short-term debt	0
Long-term debt	0
Other liabilities	0
Separate account liabilities - investment contracts	0
Total Financial Instrument Liabilities Not Carried At Fair Value	$ 70,824

[1] (1) Carrying values presented herein differ from those in the Company’s Unaudited Interim Statement of Financial Position because certain items within the respective financial statement captions are not considered financial instruments or out of scope under authoritative guidance relating to disclosures of the fair value of financial instruments. Financial statement captions excluded from the above table are not considered financial instruments.