Fair Value of Assets and Liabilities (Financial Instruments where Carrying Amounts and Fair Values May Differ) (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018	Jun. 30, 2018	Dec. 31, 2017
Assets:
Policy loans	$ 12,239	$ 12,805
Cash and cash equivalents	3,998,400	4,503,534	$ 1,380,913	$ 1,639,939
Accrued investment income	98,149	90,895
Reinsurance recoverables	646,139	572,102
Receivables from parent and affiliates	15,172	46,381
Liabilities:
Cash collateral for loaned securities	0	384
Short-term debt	0	140,569
Long-term debt	653,596	787,596
Reinsurance payables	251,804	232,937
Fair Value
Assets:
Commercial mortgage and other loans	1,358,041	1,339,707
Policy loans	12,239	12,805
Short-term investments	0	7,750
Cash and cash equivalents	1,303,660	811,175
Accrued investment income	98,149	90,895
Reinsurance recoverables	53,251	55,236
Receivables from parent and affiliates	11,974	9,188
Other assets	5,633	3,735
Total assets	2,842,947	2,330,491
Liabilities:
Policyholders’ account balances - investment contracts	1,003,487	560,548
Cash collateral for loaned securities	0	384
Short-term debt	0	139,843
Long-term debt	682,141	791,670
Reinsurance payables	53,251	55,236
Payables to parent and affiliates	35,557	30,846
Other liabilities	155,474	554,162
Separate account liabilities - investment contracts	65	71
Total liabilities	1,929,975	2,132,760
Carrying Amount
Assets:
Commercial mortgage and other loans	1,316,611	1,353,478
Policy loans	12,239	12,805
Short-term investments	0	7,750
Cash and cash equivalents	1,303,660	811,175
Accrued investment income	98,149	90,895
Reinsurance recoverables	53,251	55,236
Receivables from parent and affiliates	11,974	9,188
Other assets	5,633	3,735
Total assets	2,801,517	2,344,262
Liabilities:
Policyholders’ account balances - investment contracts	997,938	565,903
Cash collateral for loaned securities	0	384
Short-term debt	0	140,569
Long-term debt	653,596	787,596
Reinsurance payables	53,251	55,236
Payables to parent and affiliates	35,557	30,846
Other liabilities	155,474	554,162
Separate account liabilities - investment contracts	65	71
Total liabilities	1,895,881	2,134,767
Level 1 | Fair Value
Assets:
Commercial mortgage and other loans	0	0
Policy loans	0	0
Short-term investments	0	7,750
Cash and cash equivalents	468,660	136,175
Accrued investment income	0	0
Reinsurance recoverables	0	0
Receivables from parent and affiliates	0	0
Other assets	0	0
Total assets	468,660	143,925
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
Level 2 | Fair Value
Assets:
Commercial mortgage and other loans	0	0
Policy loans	0	0
Short-term investments	0	0
Cash and cash equivalents	835,000	675,000
Accrued investment income	98,149	90,895
Reinsurance recoverables	0	0
Receivables from parent and affiliates	11,974	9,188
Other assets	5,633	3,735
Total assets	950,756	778,818
Liabilities:
Policyholders’ account balances - investment contracts	0	0
Cash collateral for loaned securities	0	384
Short-term debt	0	139,843
Long-term debt	682,141	791,670
Reinsurance payables	0	0
Payables to parent and affiliates	35,557	30,846
Other liabilities	155,474	554,162
Separate account liabilities - investment contracts	65	71
Total liabilities	873,237	1,516,976
Level 3 | Fair Value
Assets:
Commercial mortgage and other loans	1,358,041	1,339,707
Policy loans	12,239	12,805
Short-term investments	0	0
Cash and cash equivalents	0	0
Accrued investment income	0	0
Reinsurance recoverables	53,251	55,236
Receivables from parent and affiliates	0	0
Other assets	0	0
Total assets	1,423,531	1,407,748
Liabilities:
Policyholders’ account balances - investment contracts	1,003,487	560,548
Cash collateral for loaned securities	0	0
Short-term debt	0	0
Long-term debt	0	0
Reinsurance payables	53,251	55,236
Payables to parent and affiliates	0	0
Other liabilities	0	0
Separate account liabilities - investment contracts	0	0
Total liabilities	$ 1,056,738	$ 615,784