Fair Value of Assets and Liabilities (Financial Instruments where Carrying Amounts and Fair Values May Differ) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Assets:
Policy loans	$ 11,806	$ 12,366
Short-term investments	318,161	335,358
Cash and cash equivalents	1,069,211	2,795,163
Accrued investment income	121,604	102,724
Reinsurance recoverables	694,040	621,510
Receivables from parent and affiliates	87,620	62,765
Liabilities:
Short-term debt	119,671	242,094
Reinsurance payables	178,860	235,318
Fair Value
Assets:
Commercial mortgage and other loans	1,836,633	1,512,283
Policy loans	11,806	12,366
Short-term investments	165,000	75,004
Cash and cash equivalents	536,078	989,558
Accrued investment income	121,604	102,724
Reinsurance recoverables	51,225	56,171
Receivables from parent and affiliates	31,594	60,779
Other assets	672,424	64,999
Total assets	3,426,364	2,873,884
Liabilities:
Policyholders’ account balances - investment contracts	2,426,471	1,445,486
Short-term debt	121,205	245,617
Long-term debt	332,451	446,105
Reinsurance payables	44,446	50,035
Payables to parent and affiliates	47,345	39,209
Other liabilities	757,968	205,988
Separate account liabilities - investment contracts	30	54
Total liabilities	3,729,916	2,432,494
Carrying Amount
Assets:
Commercial mortgage and other loans	1,765,770	1,471,522
Policy loans	11,806	12,366
Short-term investments	165,000	75,004
Cash and cash equivalents	536,078	989,558
Accrued investment income	121,604	102,724
Reinsurance recoverables	50,484	55,796
Receivables from parent and affiliates	31,594	60,192
Other assets	672,424	64,999
Total assets	3,354,760	2,832,161
Liabilities:
Policyholders’ account balances - investment contracts	2,406,100	1,438,742
Short-term debt	119,671	242,094
Long-term debt	299,747	419,418
Reinsurance payables	44,446	50,035
Payables to parent and affiliates	47,345	39,209
Other liabilities	757,968	205,988
Separate account liabilities - investment contracts	30	54
Total liabilities	3,675,307	2,395,540
Level 1 | Fair Value
Assets:
Commercial mortgage and other loans	0	0
Policy loans	0	0
Short-term investments	165,000	75,004
Cash and cash equivalents	386,078	687,558
Accrued investment income	0	0
Reinsurance recoverables	0	0
Receivables from parent and affiliates	0	0
Other assets	0	0
Total assets	551,078	762,562
Liabilities:
Policyholders’ account balances - investment contracts	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	150,000	302,000
Accrued investment income	121,604	102,724
Reinsurance recoverables	0	0
Receivables from parent and affiliates	31,594	10,192
Other assets	278,355	1,893
Total assets	581,553	416,809
Liabilities:
Policyholders’ account balances - investment contracts	0	0
Short-term debt	121,205	245,617
Long-term debt	332,451	446,105
Reinsurance payables	0	0
Payables to parent and affiliates	47,345	39,209
Other liabilities	757,968	205,988
Separate account liabilities - investment contracts	30	54
Total liabilities	1,258,999	936,973
Level 3 | Fair Value
Assets:
Commercial mortgage and other loans	1,836,633	1,512,283
Policy loans	11,806	12,366
Short-term investments	0	0
Cash and cash equivalents	0	0
Accrued investment income	0	0
Reinsurance recoverables	51,225	56,171
Receivables from parent and affiliates	0	50,587
Other assets	394,069	63,106
Total assets	2,293,733	1,694,513
Liabilities:
Policyholders’ account balances - investment contracts	2,426,471	1,445,486
Short-term debt	0	0
Long-term debt	0	0
Reinsurance payables	44,446	50,035
Payables to parent and affiliates	0	0
Other liabilities	0	0
Separate account liabilities - investment contracts	0	0
Total liabilities	$ 2,470,917	$ 1,495,521