Fair Value of Assets and Liabilities (Financial Instruments where Carrying Amounts and Fair Values May Differ) (Details) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Assets:
Policy loans	$ 1,141,331	$ 1,143,303
Accrued investment income	104,075	100,031
Liabilities:
Cash collateral for loaned securities	5,317	40,416
Short-term debt	180,500	180,000
Long-term debt	1,204,000	1,204,000
Fair Value
Assets:
Commercial mortgage and other loans	1,728,975	1,710,491
Policy loans	1,141,331	1,143,303
Cash and cash equivalents	289,559	175,361
Accrued investment income	104,075	100,031
Receivables from parent and affiliates	68,009	65,628
Other assets	36,060	6,162
Total assets	3,368,009	3,200,976
Liabilities:
Policyholders’ account balances - investment contracts	1,235,837	1,184,744
Cash collateral for loaned securities	5,317	40,416
Short-term debt	180,335	180,105
Long-term debt	1,237,111	1,227,110
Payables to parent and affiliates	70,195	72,791
Other liabilities	291,029	343,089
Total liabilities	3,019,824	3,048,255
Fair Value | Accounting Standards Update 2015-07
Liabilities:
Cost Method Investments, Fair Value Disclosure	31,000	27,000
Fair Value | Level 1
Assets:
Commercial mortgage and other loans	0	0
Policy loans	0	0
Cash and cash equivalents	26,937	19,297
Accrued investment income	0	0
Receivables from parent and affiliates	0	0
Other assets	0	0
Total assets	26,937	19,297
Liabilities:
Policyholders’ account balances - investment contracts	0	0
Cash collateral for loaned securities	0	0
Short-term debt	0	0
Long-term debt	0	0
Payables to parent and affiliates	0	0
Other liabilities	0	0
Total liabilities	0	0
Fair Value | Level 2
Assets:
Commercial mortgage and other loans	8,394	8,540
Policy loans	0	0
Cash and cash equivalents	262,622	156,064
Accrued investment income	104,075	100,031
Receivables from parent and affiliates	68,009	65,628
Other assets	36,060	6,162
Total assets	479,160	336,425
Liabilities:
Policyholders’ account balances - investment contracts	994,880	947,853
Cash collateral for loaned securities	5,317	40,416
Short-term debt	180,335	180,105
Long-term debt	1,237,111	1,227,110
Payables to parent and affiliates	70,195	72,791
Other liabilities	291,029	343,089
Total liabilities	2,778,867	2,811,364
Fair Value | Level 3
Assets:
Commercial mortgage and other loans	1,720,581	1,701,951
Policy loans	1,141,331	1,143,303
Cash and cash equivalents	0	0
Accrued investment income	0	0
Receivables from parent and affiliates	0	0
Other assets	0	0
Total assets	2,861,912	2,845,254
Liabilities:
Policyholders’ account balances - investment contracts	240,957	236,891
Cash collateral for loaned securities	0	0
Short-term debt	0	0
Long-term debt	0	0
Payables to parent and affiliates	0	0
Other liabilities	0	0
Total liabilities	240,957	236,891
Carrying Amount
Assets:
Commercial mortgage and other loans	1,641,942	1,658,235
Policy loans	1,141,331	1,143,303
Cash and cash equivalents	289,559	175,361
Accrued investment income	104,075	100,031
Receivables from parent and affiliates	68,009	65,628
Other assets	36,060	6,162
Total assets	3,280,976	3,148,720
Liabilities:
Policyholders’ account balances - investment contracts	1,240,597	1,190,596
Cash collateral for loaned securities	5,317	40,416
Short-term debt	180,500	180,000
Long-term debt	1,204,000	1,204,000
Payables to parent and affiliates	70,195	72,791
Other liabilities	291,029	343,089
Total liabilities	2,991,638	3,030,892
Carrying Amount | Accounting Standards Update 2015-07
Liabilities:
Cost Method Investments, Fair Value Disclosure	$ 29,000	$ 26,000