Fair Value of Assets and Liabilities (Financial Instruments where Carrying Amounts and Fair Values May Differ) (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018	Dec. 31, 2017
Assets:
Policy loans	$ 1,251,094	$ 1,236,077
Cash and cash equivalents	403,283	416,840	$ 81,186	$ 212,569
Accrued investment income	89,358	88,278
Receivables from parent and affiliates	278,050	289,580
Liabilities:
Cash collateral for loaned securities	10,334	11,063
Fair Value
Assets:
Commercial mortgage and other loans	1,240,689	1,214,350
Policy loans	1,251,094	1,236,077
Cash and cash equivalents	48,115	199,894
Accrued investment income	89,358	88,278
Receivables from parent and affiliates	149,571	154,938
Other assets	35,112	28,950
Total assets	2,813,939	2,922,487
Liabilities:
Policyholders’ account balances - investment contracts	1,502,794	1,479,069
Cash collateral for loaned securities	10,334	11,063
Payables to parent and affiliates	217,073	229,345
Other liabilities	358,256	372,997
Total liabilities	2,088,457	2,092,474
Carrying Amount
Assets:
Commercial mortgage and other loans	1,212,618	1,209,150
Policy loans	1,251,094	1,236,077
Cash and cash equivalents	48,115	199,894
Accrued investment income	89,358	88,278
Receivables from parent and affiliates	149,571	154,938
Other assets	35,112	28,950
Total assets	2,785,868	2,917,287
Liabilities:
Policyholders’ account balances - investment contracts	1,507,136	1,486,929
Cash collateral for loaned securities	10,334	11,063
Payables to parent and affiliates	217,073	229,345
Other liabilities	358,256	372,997
Total liabilities	2,092,799	2,100,334
Level 1 | Fair Value
Assets:
Commercial mortgage and other loans	0	0
Policy loans	0	0
Cash and cash equivalents	48,115	56,894
Accrued investment income	0	0
Receivables from parent and affiliates	0	0
Other assets	0	0
Total assets	48,115	56,894
Liabilities:
Policyholders’ 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	0	143,000
Accrued investment income	89,358	88,278
Receivables from parent and affiliates	149,571	154,938
Other assets	35,112	28,950
Total assets	274,041	415,166
Liabilities:
Policyholders’ account balances - investment contracts	1,226,786	1,206,747
Cash collateral for loaned securities	10,334	11,063
Payables to parent and affiliates	217,073	229,345
Other liabilities	358,256	372,997
Total liabilities	1,812,449	1,820,152
Level 3 | Fair Value
Assets:
Commercial mortgage and other loans	1,240,689	1,214,350
Policy loans	1,251,094	1,236,077
Cash and cash equivalents	0	0
Accrued investment income	0	0
Receivables from parent and affiliates	0	0
Other assets	0	0
Total assets	2,491,783	2,450,427
Liabilities:
Policyholders’ account balances - investment contracts	276,008	272,322
Cash collateral for loaned securities	0	0
Payables to parent and affiliates	0	0
Other liabilities	0	0
Total liabilities	$ 276,008	$ 272,322