Reinsurance (Reinsurance amounts included in the Statements of Operations and Comprehensive Income (Loss)) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Premiums:
Direct	$ 6,161	$ 6,522	$ 20,376	$ 22,957
Assumed	8,630	6,355	27,060	25,848
Ceded	(855)	(371)	(1,908)	(563)
Net premiums	13,936	12,506	45,528	48,242
Policy charges and fee income:
Direct	102,669	119,509	304,593	363,540
Assumed	395,381	416,389	1,161,236	1,222,535
Ceded	(8,610)	(8,746)	(23,838)	(26,201)
Net policy charges and fee income	489,440	527,152	1,441,991	1,559,874
Asset administration fees and other income:
Direct	26,244	44,616	132,081	124,587
Assumed	78,547	78,408	227,511	227,182
Ceded	(2,033)	(2,097)	(5,852)	(6,249)
Net asset administration fees and other income	102,758	120,927	353,740	345,520
Realized investment gains (losses), net:
Direct	(2,520,872)	1,644,998	1,878,766	1,404,528
Assumed	2,332,646	(2,243,942)	(6,422,045)	(4,290,175)
Ceded	(57,748)	61,677	163,850	111,946
Realized investment gains (losses), net	(245,974)	(537,267)	(4,379,429)	(2,773,701)
Policyholders' benefits (including change in reserves):
Direct	14,018	22,680	73,651	47,399
Assumed	30,844	48,154	181,079	82,130
Ceded	(1,038)	(1,001)	(6,145)	(3,856)
Net policyholders' benefits (including change in reserves)	43,824	69,833	248,585	125,673
Interest credited to policyholders’ account balances:
Direct	40,428	27,944	73,983	49,289
Assumed	43,457	30,959	89,311	55,053
Ceded	(2,601)	(1,956)	(2,294)	(3,613)
Net interest credited to policyholders’ account balances	81,284	56,947	161,000	100,729
Reinsurance expense allowances and general and administrative expenses, net of capitalization and amortization	307,043	298,565	890,849	738,045
Unaffiliated activity
Policy charges and fee income:
Ceded	(1,700)	(1,000)	(2,400)	(1,000)
Policyholders' benefits (including change in reserves):
Ceded	$ 100	$ 0	$ (300)	$ 0