Reinsurance (Reinsurance amounts included in the Statement 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	$ 468,900	$ 451,790	$ 1,408,157	$ 1,343,358
Assumed	51	57	157	175
Ceded	(466,593)	(437,696)	(1,379,545)	(1,306,564)
Net premiums	2,358	14,151	28,769	36,969
Policy charges and fee income:
Direct	896,151	843,551	2,856,071	2,407,062
Assumed	130,113	125,079	385,820	369,483
Ceded	(915,635)	(861,704)	(2,843,402)	(2,371,460)
Net policy charges and fee income	110,629	106,926	398,489	405,085
Net investment income:
Direct	96,424	87,260	297,931	249,366
Assumed	427	404	1,230	1,162
Ceded	(1,595)	(1,478)	(5,093)	(4,778)
Net investment income	95,256	86,186	294,068	245,750
Asset administration fees:
Direct	90,797	88,721	262,616	262,449
Assumed	0	0	0	0
Ceded	(86,661)	(84,994)	(250,862)	(251,705)
Net asset administration fees	4,136	3,727	11,754	10,744
Other income:
Direct	19,631	20,432	59,459	49,778
Assumed	438	57	(1,033)	(133)
Ceded	(7)	(219)	(69)	(46)
Amortization of reinsurance income	1,180	1,493	(1,160)	7,538
Net other income	21,242	21,763	57,197	57,137
Realized investment gains (losses), net:
Direct	(2,500,567)	1,234,853	(4,920,019)	3,213,137
Assumed	0	0	0	0
Ceded	2,540,151	(1,284,276)	4,858,718	(3,348,492)
Realized investment gains (losses), net	39,584	(49,423)	(61,301)	(135,355)
Policyholders’ benefits (including change in reserves):
Direct	874,424	636,021	2,671,720	1,932,194
Assumed	252,424	122,727	747,135	381,934
Ceded	(1,080,958)	(748,925)	(3,287,196)	(2,212,128)
Net policyholders’ benefits (including change in reserves)	45,890	9,823	131,659	102,000
Interest credited to policyholders’ account balances:
Direct	163,479	137,309	376,590	383,521
Assumed	35,575	34,414	100,744	105,780
Ceded	(119,647)	(127,014)	(303,020)	(361,239)
Net interest credited to policyholders’ account balances	79,407	44,709	174,314	128,062
Reinsurance expense allowances and general and administrative expenses, net of capitalization and amortization	(475,041)	(420,813)	(1,393,034)	(1,200,005)
Unaffiliated activity
Premiums:
Assumed	100	100	200	200
Ceded	(100)	(100)	(300)	(100)
Policy charges and fee income:
Ceded	(13,000)	(8,000)	(25,000)	(14,000)
Other income:
Assumed	1,000	(100)	(1,000)	(100)
Realized investment gains (losses), net:
Ceded	61,000	(33,000)	117,000	(81,000)
Policyholders’ benefits (including change in reserves):
Assumed	1,000	100	1,000	0
Ceded	$ (8,000)	$ (4,000)	$ (12,000)	$ (8,000)