Fair Value of Assets and Liabilities (Financial Instruments where Carrying Amounts and Fair Values May Differ) (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012		Dec. 31, 2011
Assets:
Policy loans	$ 12,065		$ 14,316
Accrued investment income	52,574		59,033
Liabilities:
Cash collateral for loaned securities	48,371		125,884
Short-term debt	83,502		27,803
Long-term debt	600,000		600,000
Carrying (Reported) Amount, Fair Value Disclosure [Member]
Assets:
Commercial mortgage and other loans	461,186	[1]	449,359
Policy loans	12,065	[1]	14,316
Cash	438	[1]	749
Accrued investment income	52,574	[1]	59,033
Other assets	13,352	[1]	12,237
Total Assets Financial Instruments Not Carried At Fair Value	539,615	[1]	535,694
Liabilities:
Investment contracts- policyholders' account balances	71,895	[1]	66,176
Cash collateral for loaned securities	48,371	[1]	125,884
Short-term debt	83,502	[1]	27,803
Long-term debt	600,000	[1]	600,000
Other liabilities	137,693	[1]	169,139
Separate account liabilities - investment contracts	1,030	[1]	1,192
Total Financial Instrument Liabilities Not Carried At Fair Value	942,491	[1]	990,194
Estimate of Fair Value, Fair Value Disclosure [Member]
Assets:
Commercial mortgage and other loans	511,077		490,151
Policy loans	12,065		14,316
Cash	438		749
Accrued investment income	52,574		59,033
Other assets	13,352		12,237
Total Assets Financial Instruments Not Carried At Fair Value	589,506		576,486
Liabilities:
Investment contracts- policyholders' account balances	74,331		66,659
Cash collateral for loaned securities	48,371		125,884
Short-term debt	83,502		27,803
Long-term debt	642,557		627,415
Other liabilities	137,693		169,139
Separate account liabilities - investment contracts	1,030		1,192
Total Financial Instrument Liabilities Not Carried At Fair Value	987,484		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	438
Accrued investment income	0
Other assets	0
Total Assets Financial Instruments Not Carried At Fair Value	438
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	52,574
Other assets	13,352
Total Assets Financial Instruments Not Carried At Fair Value	65,926
Liabilities:
Investment contracts- policyholders' account balances	0
Cash collateral for loaned securities	48,371
Short-term debt	83,502
Long-term debt	642,557
Other liabilities	137,693
Separate account liabilities - investment contracts	1,030
Total Financial Instrument Liabilities Not Carried At Fair Value	913,153
Estimate of Fair Value, Fair Value Disclosure [Member] | Fair Value, Inputs, Level 3 [Member]
Assets:
Commercial mortgage and other loans	511,077
Policy loans	12,065
Cash	0
Accrued investment income	0
Other assets	0
Total Assets Financial Instruments Not Carried At Fair Value	523,142
Liabilities:
Investment contracts- policyholders' account balances	74,331
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	$ 74,331

[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.