Reinsurance and Policy Provisions (Amounts Ceded to Equitrust and Athene, Impact on Consolidated Statements of Operations and Consolidated Statements of Cash Flows) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Effects of Reinsurance [Line Items]
Annuity product charges									$ 240,035	$ 224,488	$ 200,494
Change in fair value of derivatives	$ 466,434	$ (20,042)	$ 76,045	$ 384,469	$ (1,054,281)	$ 595,311	$ 132,205	$ (451,083)	906,906	(777,848)	1,677,871
Interest sensitive and index product benefits									1,287,576	1,610,835	2,023,668
Change in fair value of embedded derivatives									1,454,042	(1,389,491)	919,735
Other operating costs and expenses									154,153	129,301	111,691
Coinsurance deposits									91,238	(23,838)	(6,597)
Coinsurance Agreements, EquiTrust and Athene
Effects of Reinsurance [Line Items]
Annuity product charges									7,792	7,074	6,458
Change in fair value of derivatives									97,195	(41,487)	94,382
Coinsurance, revenues included in consolidated statement of operations									104,987	(34,413)	100,840
Interest sensitive and index product benefits									132,127	165,485	177,332
Change in fair value of embedded derivatives									109,002	(92,649)	35,561
Other operating costs and expenses									18,778	20,415	19,877
Coinsurance, benefits and expenses included in the consolidated statement of operations									259,907	93,251	232,770
Annuity deposits									(290,040)	(413,222)	(387,280)
Cash payments to policyholders									381,276	389,384	380,683
Coinsurance deposits									$ 91,236	$ (23,838)	$ (6,597)