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, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Premiums:
Direct	$ 7,582	$ 8,028	$ 27,519	$ 26,216
Assumed	6,568	5,849	22,714	25,402
Ceded	(471)	(1,372)	(2,225)	(2,952)
Net premiums	13,679	12,505	48,008	48,666
Policy charges and fee income:
Direct	137,719	153,835	423,170	469,128
Assumed	422,888	413,400	1,260,550	1,210,789
Ceded	(10,015)	(11,328)	(30,495)	(33,607)
Net policy charges and fee income	550,592	555,907	1,653,225	1,646,310
Asset administration fees and other income:
Direct	18,360	30,573	70,053	97,972
Assumed	77,276	74,586	228,423	216,697
Ceded	(2,316)	(2,446)	(7,016)	(7,285)
Net asset administration fees and other income	93,320	102,713	291,460	307,384
Realized investment gains (losses), net:
Direct	(1,033,002)	(32,663)	(2,239,254)	(779,499)
Assumed	1,133,110	1,237,967	2,965,558	470,545
Ceded	(34,835)	(35,227)	(92,482)	(18,558)
Realized investment gains (losses), net	65,273	1,170,077	633,822	(327,512)
Policyholders' benefits (including change in reserves):
Direct	20,847	10,061	51,364	36,627
Assumed	29,743	6,114	64,401	28,505
Ceded	(659)	(2,119)	(2,141)	15,119
Net policyholders' benefits (including change in reserves)	49,931	14,056	113,624	80,251
Interest credited to policyholders’ account balances:
Direct	41,949	42,401	113,522	(5,421)
Assumed	43,662	52,559	109,210	9,108
Ceded	(3,298)	(4,461)	(8,829)	(3,120)
Net interest credited to policyholders’ account balances	82,313	90,499	213,903	567
Reinsurance expense allowances and general and administrative expenses, net of capitalization and amortization	283,512	352,114	875,265	524,961
Unaffiliated activity
Policy charges and fee income:
Ceded	(400)	(600)	(1,000)	(2,000)
Policyholders' benefits (including change in reserves):
Ceded	$ 0	$ 0	$ (200)	$ 0