Reinsurance (Reinsurance amounts included in the Statement 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	$ 476,986	$ 449,613	$ 939,257	$ 891,568
Assumed	52	58	106	118
Ceded	(464,621)	(434,768)	(912,952)	(868,868)
Net premiums	12,417	14,903	26,411	22,818
Policy charges and fee income:
Direct	1,106,725	717,264	1,959,920	1,563,511
Assumed	128,748	122,695	255,707	244,404
Ceded	(1,086,802)	(670,955)	(1,927,767)	(1,509,756)
Net policy charges and fee income	148,671	169,004	287,860	298,159
Net investment income:
Direct	106,949	82,957	201,507	162,106
Assumed	407	385	803	758
Ceded	(1,794)	(1,693)	(3,498)	(3,300)
Net investment income	105,562	81,649	198,812	159,564
Asset administration fees:
Direct	87,951	86,695	171,819	173,728
Assumed	0	0	0	0
Ceded	(83,990)	(83,151)	(164,201)	(166,711)
Net asset administration fees	3,961	3,544	7,618	7,017
Other income:
Direct	20,030	12,093	39,828	29,346
Assumed	(1,271)	(100)	(1,471)	(190)
Ceded	(39)	226	(62)	173
Amortization of reinsurance income	(3,722)	3,859	(2,340)	6,045
Net other income	14,998	16,078	35,955	35,374
Realized investment gains (losses), net:
Direct	(1,783,941)	503,522	(2,419,452)	1,978,284
Assumed	0	0	0	0
Ceded	1,731,691	(540,412)	2,318,567	(2,064,216)
Realized investment gains (losses), net	(52,250)	(36,890)	(100,885)	(85,932)
Policyholders’ benefits (including change in reserves):
Direct	1,150,985	644,501	1,797,296	1,296,173
Assumed	282,961	146,405	494,711	259,207
Ceded	(1,387,655)	(750,465)	(2,206,238)	(1,463,203)
Net policyholders’ benefits (including change in reserves)	46,291	40,441	85,769	92,177
Interest credited to policyholders’ account balances:
Direct	118,420	121,478	213,111	246,212
Assumed	34,512	34,849	65,169	71,366
Ceded	(102,222)	(113,772)	(183,373)	(234,225)
Net interest credited to policyholders’ account balances	50,710	42,555	94,907	83,353
Reinsurance expense allowances and general and administrative expenses, net of capitalization and amortization	(573,978)	(345,280)	(917,993)	(779,192)
Unaffiliated activity
Premiums:
Assumed	0	0	100	100
Ceded	(100)	0	(200)	0
Policy charges and fee income:
Ceded	(7,000)	(4,000)	(12,000)	(6,000)
Other income:
Assumed	(1,000)	(100)	(2,000)	(200)
Realized investment gains (losses), net:
Ceded	42,000	(10,000)	56,000	(48,000)
Policyholders’ benefits (including change in reserves):
Assumed	0	0	(200)	(100)
Ceded	$ (2,000)	$ (2,000)	$ (4,000)	$ (4,000)