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, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Premiums:
Direct	$ 451,790	$ 428,684	$ 1,343,358	$ 1,280,293
Assumed	57	63	175	194
Ceded	(437,696)	(413,623)	(1,306,564)	(1,242,529)
Net premiums	14,151	15,124	36,969	37,958
Policy charges and fee income:
Direct	843,551	816,191	2,407,062	2,593,583
Assumed	125,079	127,493	369,483	351,464
Ceded	(861,704)	(814,579)	(2,371,460)	(2,804,107)
Net policy charges and fee income	106,926	129,105	405,085	140,940
Net investment income:
Direct	87,260	87,605	249,366	269,999
Assumed	404	376	1,162	1,104
Ceded	(1,478)	(1,459)	(4,778)	(3,925)
Net investment income	86,186	86,522	245,750	267,178
Asset administration fees:
Direct	88,721	86,716	262,449	251,709
Assumed	0	0	0	0
Ceded	(84,994)	(82,161)	(251,705)	(238,577)
Net asset administration fees	3,727	4,555	10,744	13,132
Other income:
Direct	20,432	16,678	49,778	46,617
Assumed	57	(25)	(133)	184
Ceded	(219)	19	(46)	(4)
Amortization of reinsurance income	1,493	1,348	7,538	1,348
Net other income	21,763	18,020	57,137	48,145
Realized investment gains (losses), net:
Direct	1,234,853	1,390,083	3,213,137	442,408
Assumed	0	0	0	0
Ceded	(1,284,276)	(1,665,269)	(3,348,492)	(473,583)
Realized investment gains (losses), net	(49,423)	(275,186)	(135,355)	(31,175)
Policyholders’ benefits (including change in reserves):
Direct	636,021	560,252	1,932,194	1,787,338
Assumed	122,727	154,389	381,934	402,025
Ceded	(748,925)	(659,697)	(2,212,128)	(2,247,598)
Net policyholders’ benefits (including change in reserves)	9,823	54,944	102,000	(58,235)
Interest credited to policyholders’ account balances:
Direct	137,309	139,715	383,521	249,063
Assumed	34,414	33,858	105,780	101,687
Ceded	(127,014)	(135,377)	(361,239)	(221,827)
Net interest credited to policyholders’ account balances	44,709	38,196	128,062	128,923
Reinsurance expense allowances and general and administrative expenses, net of capitalization and amortization	(420,813)	(502,172)	(1,200,005)	(968,627)
Unaffiliated activity
Premiums:
Assumed	100	100	200	200
Ceded	(100)	0	(100)	0
Policy charges and fee income:
Ceded	(8,000)	(4,000)	(14,000)	(5,000)
Other income:
Assumed	(100)	0	(100)	200
Realized investment gains (losses), net:
Ceded	(33,000)	(49,000)	(81,000)	(26,000)
Policyholders’ benefits (including change in reserves):
Assumed	100	0	0	400
Ceded	$ (4,000)	$ (1,000)	$ (8,000)	$ 5,000