Fair Value of Assets and Liabilities (Financial Instruments where Carrying Amounts and Fair Values May Differ) (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Assets:
Policy loans	$ 12,319	$ 12,719
Accrued investment income	68,810	86,004
Receivables from parent and affiliates	100,570	111,703
Liabilities:
Cash collateral for loaned securities	35,297	23,350
Short-term debt	37,710	28,101
Long-term debt	971,899	971,899
Reinsurance payables	268,455	275,822
Fair Value
Assets:
Commercial mortgage and other loans	1,284,824	1,235,842
Policy loans	12,319	12,719
Short-term investments	0	35,000
Cash and cash equivalents	65,982	261,886
Accrued investment income	68,810	86,004
Reinsurance recoverables	62,867	63,775
Receivables from parent and affiliates	59,581	70,779
Other assets	47,629	53,858
Total assets	1,602,012	1,819,863
Liabilities:
Policyholders’ account balances - investment contracts	257,400	247,986
Cash collateral for loaned securities	35,297	23,350
Short-term debt	39,616	28,146
Long-term debt	997,433	994,198
Reinsurance payables	62,867	63,775
Payables to parent and affiliates	95,097	91,432
Other liabilities	172,294	189,366
Separate account liabilities - investment contracts	162	187
Total liabilities	1,660,166	1,638,440
Fair Value | Measurement at NAV per share
Liabilities:
Cost Method Investments, Fair Value Disclosure	3,500	3,400
Fair Value | Level 1
Assets:
Commercial mortgage and other loans	0	0
Policy loans	0	0
Short-term investments	0	0
Cash and cash equivalents	65,982	6,886
Accrued investment income	0	0
Reinsurance recoverables	0	0
Receivables from parent and affiliates	0	0
Other assets	0	0
Total assets	65,982	6,886
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
Reinsurance payables	0	0
Payables to parent and affiliates	0	0
Other liabilities	0	0
Separate account liabilities - investment contracts	0	0
Total liabilities	0	0
Fair Value | Level 2
Assets:
Commercial mortgage and other loans	0	0
Policy loans	0	0
Short-term investments	0	35,000
Cash and cash equivalents	0	255,000
Accrued investment income	68,810	86,004
Reinsurance recoverables	0	0
Receivables from parent and affiliates	59,581	70,779
Other assets	47,629	53,858
Total assets	176,020	500,641
Liabilities:
Policyholders’ account balances - investment contracts	0	0
Cash collateral for loaned securities	35,297	23,350
Short-term debt	39,616	28,146
Long-term debt	997,433	994,198
Reinsurance payables	0	0
Payables to parent and affiliates	95,097	91,432
Other liabilities	172,294	189,366
Separate account liabilities - investment contracts	162	187
Total liabilities	1,339,899	1,326,679
Fair Value | Level 3
Assets:
Commercial mortgage and other loans	1,284,824	1,235,842
Policy loans	12,319	12,719
Short-term investments	0	0
Cash and cash equivalents	0	0
Accrued investment income	0	0
Reinsurance recoverables	62,867	63,775
Receivables from parent and affiliates	0	0
Other assets	0	0
Total assets	1,360,010	1,312,336
Liabilities:
Policyholders’ account balances - investment contracts	257,400	247,986
Cash collateral for loaned securities	0	0
Short-term debt	0	0
Long-term debt	0	0
Reinsurance payables	62,867	63,775
Payables to parent and affiliates	0	0
Other liabilities	0	0
Separate account liabilities - investment contracts	0	0
Total liabilities	320,267	311,761
Carrying Amount
Assets:
Commercial mortgage and other loans	1,275,084	1,231,893
Policy loans	12,319	12,719
Short-term investments	0	35,000
Cash and cash equivalents	65,982	261,886
Accrued investment income	68,810	86,004
Reinsurance recoverables	62,867	63,775
Receivables from parent and affiliates	59,581	70,779
Other assets	47,629	53,858
Total assets	1,592,272	1,815,914
Liabilities:
Policyholders’ account balances - investment contracts	259,053	250,493
Cash collateral for loaned securities	35,297	23,350
Short-term debt	37,710	28,101
Long-term debt	971,899	971,899
Reinsurance payables	62,867	63,775
Payables to parent and affiliates	95,097	91,432
Other liabilities	172,294	189,366
Separate account liabilities - investment contracts	162	187
Total liabilities	1,634,379	1,618,603
Carrying Amount | Measurement at NAV per share
Liabilities:
Cost Method Investments, Fair Value Disclosure	$ 3,100	$ 3,100