Fair Value of Assets and Liabilities (Financial Instruments where Carrying Amounts and Fair Values May Differ) (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Assets:
Policy loans	$ 12,251	$ 12,366
Cash and cash equivalents	13,945,360	2,795,163
Accrued investment income	107,400	102,724
Reinsurance recoverables	944,229	621,510
Receivables from parent and affiliates	63,581	62,765
Liabilities:
Long-term debt	419,418	419,418
Reinsurance payables	285,038	235,318
Fair Value
Assets:
Commercial mortgage and other loans	1,517,044	1,512,283
Policy loans	12,251	12,366
Short-term investments	480,000	75,004
Cash and cash equivalents	2,125,451	989,558
Accrued investment income	107,400	102,724
Reinsurance recoverables	55,626	56,171
Receivables from parent and affiliates	11,128	60,779
Other assets	136,869	64,999
Total assets	4,445,769	2,873,884
Liabilities:
Policyholders’ account balances - investment contracts	1,622,012	1,445,486
Cash collateral for loaned securities	0	0
Short-term debt	235,228	245,617
Long-term debt	428,943	446,105
Reinsurance payables	48,544	50,035
Payables to parent and affiliates	49,200	39,209
Other liabilities	624,319	205,988
Separate account liabilities - investment contracts	39	54
Total liabilities	3,008,285	2,432,494
Carrying Amount
Assets:
Commercial mortgage and other loans	1,502,846	1,471,522
Policy loans	12,251	12,366
Short-term investments	480,000	75,004
Cash and cash equivalents	2,125,451	989,558
Accrued investment income	107,400	102,724
Reinsurance recoverables	55,137	55,796
Receivables from parent and affiliates	11,128	60,192
Other assets	136,869	64,999
Total assets	4,431,082	2,832,161
Liabilities:
Policyholders’ account balances - investment contracts	1,615,833	1,438,742
Cash collateral for loaned securities	0	0
Short-term debt	234,178	242,094
Long-term debt	419,418	419,418
Reinsurance payables	48,544	50,035
Payables to parent and affiliates	49,200	39,209
Other liabilities	624,319	205,988
Separate account liabilities - investment contracts	39	54
Total liabilities	2,991,531	2,395,540
Level 1 | Fair Value
Assets:
Commercial mortgage and other loans	0	0
Policy loans	0	0
Short-term investments	480,000	75,004
Cash and cash equivalents	2,025,451	687,558
Accrued investment income	0	0
Reinsurance recoverables	0	0
Receivables from parent and affiliates	0	0
Other assets	0	0
Total assets	2,505,451	762,562
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	100,000	302,000
Accrued investment income	107,400	102,724
Reinsurance recoverables	0	0
Receivables from parent and affiliates	11,128	10,192
Other assets	7,274	1,893
Total assets	225,802	416,809
Liabilities:
Policyholders’ account balances - investment contracts	0	0
Cash collateral for loaned securities	0	0
Short-term debt	235,228	245,617
Long-term debt	428,943	446,105
Reinsurance payables	0	0
Payables to parent and affiliates	49,200	39,209
Other liabilities	624,319	205,988
Separate account liabilities - investment contracts	39	54
Total liabilities	1,337,729	936,973
Level 3 | Fair Value
Assets:
Commercial mortgage and other loans	1,517,044	1,512,283
Policy loans	12,251	12,366
Short-term investments	0	0
Cash and cash equivalents	0	0
Accrued investment income	0	0
Reinsurance recoverables	55,626	56,171
Receivables from parent and affiliates	0	50,587
Other assets	129,595	63,106
Total assets	1,714,516	1,694,513
Liabilities:
Policyholders’ account balances - investment contracts	1,622,012	1,445,486
Cash collateral for loaned securities	0	0
Short-term debt	0	0
Long-term debt	0	0
Reinsurance payables	48,544	50,035
Payables to parent and affiliates	0	0
Other liabilities	0	0
Separate account liabilities - investment contracts	0	0
Total liabilities	$ 1,670,556	$ 1,495,521