Fair Value of Assets and Liabilities (Financial Instruments where Carrying Amounts and Fair Values May Differ) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Assets:
Policy loans	$ 1,236,077	$ 1,161,101
Cash and cash equivalents	416,840	212,569	$ 96,157	$ 370,286
Accrued investment income	88,278	82,341
Receivables from parent and affiliates	289,580	300,116
Liabilities:
Cash collateral for loaned securities	11,063	33,169
Fair Value
Assets:
Commercial mortgage and other loans	1,214,350	1,111,625
Policy loans	1,236,077	1,161,101
Cash and cash equivalents	199,894	184,562
Accrued investment income	88,278	82,341
Receivables from parent and affiliates	154,938	167,545
Other assets	28,950	50,407
Total Assets	2,922,487	2,757,581
Liabilities:
Policyholder account balances - investment contracts	1,479,069	1,455,018
Cash collateral for loaned securities	11,063	33,169
Payables to parent and affiliates	229,345	223,550
Other liabilities	372,997	362,592
Total liabilities	2,092,474	2,074,329
Carrying Amount
Assets:
Commercial mortgage and other loans	1,209,150	1,083,419
Policy loans	1,236,077	1,161,101
Cash and cash equivalents	199,894	184,562
Accrued investment income	88,278	82,341
Receivables from parent and affiliates	154,938	167,545
Other assets	28,950	50,407
Total Assets	2,917,287	2,729,375
Liabilities:
Policyholder account balances - investment contracts	1,486,929	1,458,599
Cash collateral for loaned securities	11,063	33,169
Payables to parent and affiliates	229,345	223,550
Other liabilities	372,997	362,592
Total liabilities	2,100,334	2,077,910
Level 1 | Fair Value
Assets:
Commercial mortgage and other loans	0	0
Policy loans	0	0
Cash and cash equivalents	56,894	36,562
Accrued investment income	0	0
Receivables from parent and affiliates	0	0
Other assets	0	0
Total Assets	56,894	36,562
Liabilities:
Policyholder account balances - investment contracts	0	0
Cash collateral for loaned securities	0	0
Payables to parent and affiliates	0	0
Other liabilities	0	0
Total liabilities	0	0
Level 2 | Fair Value
Assets:
Commercial mortgage and other loans	0	0
Policy loans	0	0
Cash and cash equivalents	143,000	148,000
Accrued investment income	88,278	82,341
Receivables from parent and affiliates	154,938	167,545
Other assets	28,950	50,407
Total Assets	415,166	448,293
Liabilities:
Policyholder account balances - investment contracts	1,206,747	1,178,583
Cash collateral for loaned securities	11,063	33,169
Payables to parent and affiliates	229,345	223,550
Other liabilities	372,997	362,592
Total liabilities	1,820,152	1,797,894
Level 3 | Fair Value
Assets:
Commercial mortgage and other loans	1,214,350	1,111,625
Policy loans	1,236,077	1,161,101
Cash and cash equivalents	0	0
Accrued investment income	0	0
Receivables from parent and affiliates	0	0
Other assets	0	0
Total Assets	2,450,427	2,272,726
Liabilities:
Policyholder account balances - investment contracts	272,322	276,435
Cash collateral for loaned securities	0	0
Payables to parent and affiliates	0	0
Other liabilities	0	0
Total liabilities	$ 272,322	276,435
Other Invested Assets | Fair Value | Measurement at NAV per share
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cost Method Investments, Fair Value Disclosure		49,000
Other Invested Assets | Carrying Amount | Measurement at NAV per share
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cost Method Investments, Fair Value Disclosure		$ 41,000