Fair Value of Assets and Liabilities (Financial Instruments where Carrying Amounts and Fair Values May Differ) (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Assets:
Commercial mortgage and other loans	$ 1,150,381	$ 1,658,235
Policy loans	1,166,456	1,143,303
Accrued investment income	87,322	100,031
Liabilities:
Securities Sold under Agreements to Repurchase	68,904	0
Cash collateral for loaned securities	74,976	40,416
Short-term debt to affiliates	0	180,000
Long-term debt to affiliates	0	1,204,000
Fair Value
Assets:
Commercial mortgage and other loans	1,181,582	1,710,491
Policy loans	1,166,456	1,143,303
Cash and cash equivalents	88,515	175,361
Accrued investment income	87,322	100,031
Receivables from parent and affiliates	76,315	65,628
Other assets	37,969	6,162
Total assets	2,638,159	3,200,976
Liabilities:
Policyholders’ account balances - investment contracts	1,382,385	1,184,744
Securities Sold under Agreements to Repurchase	68,904	0
Cash collateral for loaned securities	74,976	40,416
Short-term debt to affiliates	0	180,105
Long-term debt to affiliates	0	1,227,110
Payables to parent and affiliates	73,628	72,791
Other liabilities	305,969	343,089
Total liabilities	1,905,862	3,048,255
Fair Value | Accounting Standards Update 2015-07
Liabilities:
Cost Method Investments, Fair Value Disclosure	35,000	27,000
Fair Value | Level 1
Assets:
Commercial mortgage and other loans	0	0
Policy loans	0	0
Cash and cash equivalents	30,149	19,297
Accrued investment income	0	0
Receivables from parent and affiliates	0	0
Other assets	0	0
Total assets	30,149	19,297
Liabilities:
Policyholders’ account balances - investment contracts	0	0
Securities Sold under Agreements to Repurchase	0	0
Cash collateral for loaned securities	0	0
Short-term debt to affiliates	0	0
Long-term debt to affiliates	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	0	8,540
Policy loans	0	0
Cash and cash equivalents	58,366	156,064
Accrued investment income	87,322	100,031
Receivables from parent and affiliates	76,315	65,628
Other assets	37,969	6,162
Total assets	259,972	336,425
Liabilities:
Policyholders’ account balances - investment contracts	1,129,378	947,853
Securities Sold under Agreements to Repurchase	68,904	0
Cash collateral for loaned securities	74,976	40,416
Short-term debt to affiliates	0	180,105
Long-term debt to affiliates	0	1,227,110
Payables to parent and affiliates	73,628	72,791
Other liabilities	305,969	343,089
Total liabilities	1,652,855	2,811,364
Fair Value | Level 3
Assets:
Commercial mortgage and other loans	1,181,582	1,701,951
Policy loans	1,166,456	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	2,348,038	2,845,254
Liabilities:
Policyholders’ account balances - investment contracts	253,007	236,891
Securities Sold under Agreements to Repurchase	0	0
Cash collateral for loaned securities	0	0
Short-term debt to affiliates	0	0
Long-term debt to affiliates	0	0
Payables to parent and affiliates	0	0
Other liabilities	0	0
Total liabilities	253,007	236,891
Carrying Amount
Assets:
Commercial mortgage and other loans	1,150,381	1,658,235
Policy loans	1,166,456	1,143,303
Cash and cash equivalents	88,515	175,361
Accrued investment income	87,322	100,031
Receivables from parent and affiliates	76,315	65,628
Other assets	37,969	6,162
Total assets	2,606,958	3,148,720
Liabilities:
Policyholders’ account balances - investment contracts	1,386,099	1,190,596
Securities Sold under Agreements to Repurchase	68,904	0
Cash collateral for loaned securities	74,976	40,416
Short-term debt to affiliates	0	180,000
Long-term debt to affiliates	0	1,204,000
Payables to parent and affiliates	73,628	72,791
Other liabilities	305,969	343,089
Total liabilities	1,909,576	3,030,892
Carrying Amount | Accounting Standards Update 2015-07
Liabilities:
Cost Method Investments, Fair Value Disclosure	$ 32,000	$ 26,000