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, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Premiums:
Direct	$ 6,522	$ 7,582	$ 22,957	$ 27,519
Assumed	6,355	6,568	25,848	22,714
Ceded	(371)	(471)	(563)	(2,225)
Net premiums	12,506	13,679	48,242	48,008
Policy charges and fee income:
Direct	119,509	137,719	363,540	423,170
Assumed	416,389	422,888	1,222,535	1,260,550
Ceded	(8,746)	(10,015)	(26,201)	(30,495)
Net policy charges and fee income	527,152	550,592	1,559,874	1,653,225
Asset administration fees and other income:
Direct	44,616	18,360	124,587	70,053
Assumed	78,408	77,276	227,182	228,423
Ceded	(2,097)	(2,316)	(6,249)	(7,016)
Net asset administration fees and other income	120,927	93,320	345,520	291,460
Realized investment gains (losses), net:
Direct	1,644,998	(1,033,002)	1,404,528	(2,239,254)
Assumed	(2,243,942)	1,133,110	(4,290,175)	2,965,558
Ceded	61,677	(34,835)	111,946	(92,482)
Realized investment gains (losses), net	(537,267)	65,273	(2,773,701)	633,822
Policyholders' benefits (including change in reserves):
Direct	22,680	20,847	47,399	51,364
Assumed	48,154	29,743	82,130	64,401
Ceded	(1,001)	(659)	(3,856)	(2,141)
Net policyholders' benefits (including change in reserves)	69,833	49,931	125,673	113,624
Interest credited to policyholders’ account balances:
Direct	27,944	41,949	49,289	113,522
Assumed	30,959	43,662	55,053	109,210
Ceded	(1,956)	(3,298)	(3,613)	(8,829)
Net interest credited to policyholders’ account balances	56,947	82,313	100,729	213,903
Reinsurance expense allowances and general and administrative expenses, net of capitalization and amortization	298,565	283,512	738,045	875,265
Unaffiliated activity
Policy charges and fee income:
Ceded	(1,000)	(400)	(1,000)	(1,000)
Policyholders' benefits (including change in reserves):
Ceded	$ (0)	$ 0	$ (0)	$ (200)