Reinsurance (Reinsurance amounts included in the Statements of Operations and Comprehensive Income (Loss)) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Premiums:
Direct	$ 8,381	$ 7,824	$ 16,435	$ 19,937
Assumed	10,398	5,965	19,493	16,146
Ceded	(308)	(494)	(192)	(1,754)
Net premiums	18,471	13,295	35,736	34,329
Policy charges and fee income:
Direct	122,420	139,738	244,031	285,451
Assumed	411,058	417,636	806,146	837,662
Ceded	(8,690)	(10,031)	(17,455)	(20,480)
Net policy charges and fee income	524,788	547,343	1,032,722	1,102,633
Asset administration fees and other income:
Direct	41,226	25,660	79,971	51,693
Assumed	76,079	75,255	148,774	151,147
Ceded	(2,100)	(2,312)	(4,152)	(4,700)
Net asset administration fees and other income	115,205	98,603	224,593	198,140
Realized investment gains (losses), net:
Direct	593,738	(457,927)	(240,470)	(1,206,252)
Assumed	(1,530,524)	483,344	(2,046,233)	1,832,448
Ceded	42,571	(15,558)	50,269	(57,647)
Realized investment gains (losses), net	(894,215)	9,859	(2,236,434)	568,549
Policyholders' benefits (including change in reserves):
Direct	17,616	12,353	24,719	30,517
Assumed	31,619	16,766	33,976	34,658
Ceded	(1,345)	(452)	(2,855)	(1,482)
Net policyholders' benefits (including change in reserves)	47,890	28,667	55,840	63,693
Interest credited to policyholders’ account balances:
Direct	15,335	35,185	21,345	71,573
Assumed	19,283	29,757	24,094	65,548
Ceded	(1,263)	(2,922)	(1,657)	(5,531)
Net interest credited to policyholders’ account balances	33,355	62,020	43,782	131,590
Reinsurance expense allowances and general and administrative expenses, net of capitalization and amortization	240,225	295,556	439,480	591,753
Unaffiliated activity
Policy charges and fee income:
Ceded	(1,000)	(400)	(1,000)	(600)
Policyholders' benefits (including change in reserves):
Ceded	$ (100)	$ 0	$ (100)	$ (200)