Fair Value of Assets and Liabilities (Financial Instruments where Carrying Amounts and Fair Values May Differ) (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Assets:
Policy loans	$ 11,916	$ 12,366
Cash and cash equivalents	5,501,936	2,795,163
Accrued investment income	117,166	102,724
Reinsurance recoverables	790,715	621,510
Receivables from parent and affiliates	87,769	62,765
Liabilities:
Long-term debt	299,747	419,418
Reinsurance payables	188,463	235,318
Fair Value
Assets:
Commercial mortgage and other loans	1,745,034	1,512,283
Policy loans	11,916	12,366
Short-term investments	423,500	75,004
Cash and cash equivalents	977,811	989,558
Accrued investment income	117,166	102,724
Reinsurance recoverables	52,422	56,171
Receivables from parent and affiliates	30,863	60,779
Other assets	342,417	64,999
Total assets	3,701,129	2,873,884
Liabilities:
Policyholders’ account balances - investment contracts	2,226,866	1,445,486
Cash collateral for loaned securities	0	0
Short-term debt	379,137	245,617
Long-term debt	335,225	446,105
Reinsurance payables	45,400	50,035
Payables to parent and affiliates	42,184	39,209
Other liabilities	437,817	205,988
Separate account liabilities - investment contracts	33	54
Total liabilities	3,466,662	2,432,494
Carrying Amount
Assets:
Commercial mortgage and other loans	1,677,951	1,471,522
Policy loans	11,916	12,366
Short-term investments	423,500	75,004
Cash and cash equivalents	977,811	989,558
Accrued investment income	117,166	102,724
Reinsurance recoverables	51,665	55,796
Receivables from parent and affiliates	30,863	60,192
Other assets	342,417	64,999
Total assets	3,633,289	2,832,161
Liabilities:
Policyholders’ account balances - investment contracts	2,208,818	1,438,742
Cash collateral for loaned securities	0	0
Short-term debt	373,086	242,094
Long-term debt	299,747	419,418
Reinsurance payables	45,400	50,035
Payables to parent and affiliates	42,184	39,209
Other liabilities	437,817	205,988
Separate account liabilities - investment contracts	33	54
Total liabilities	3,407,085	2,395,540
Level 1 | Fair Value
Assets:
Commercial mortgage and other loans	0	0
Policy loans	0	0
Short-term investments	423,500	75,004
Cash and cash equivalents	977,811	687,558
Accrued investment income	0	0
Reinsurance recoverables	0	0
Receivables from parent and affiliates	0	0
Other assets	0	0
Total assets	1,401,311	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	0	302,000
Accrued investment income	117,166	102,724
Reinsurance recoverables	0	0
Receivables from parent and affiliates	30,863	10,192
Other assets	2,143	1,893
Total assets	150,172	416,809
Liabilities:
Policyholders’ account balances - investment contracts	0	0
Cash collateral for loaned securities	0	0
Short-term debt	379,137	245,617
Long-term debt	335,225	446,105
Reinsurance payables	0	0
Payables to parent and affiliates	42,184	39,209
Other liabilities	437,817	205,988
Separate account liabilities - investment contracts	33	54
Total liabilities	1,194,396	936,973
Level 3 | Fair Value
Assets:
Commercial mortgage and other loans	1,745,034	1,512,283
Policy loans	11,916	12,366
Short-term investments	0	0
Cash and cash equivalents	0	0
Accrued investment income	0	0
Reinsurance recoverables	52,422	56,171
Receivables from parent and affiliates	0	50,587
Other assets	340,274	63,106
Total assets	2,149,646	1,694,513
Liabilities:
Policyholders’ account balances - investment contracts	2,226,866	1,445,486
Cash collateral for loaned securities	0	0
Short-term debt	0	0
Long-term debt	0	0
Reinsurance payables	45,400	50,035
Payables to parent and affiliates	0	0
Other liabilities	0	0
Separate account liabilities - investment contracts	0	0
Total liabilities	$ 2,272,266	$ 1,495,521