Quarterly Financial Information (Unaudited) (Comparability of Net Income, Impact of Fair Value Accounting to Fixed Index Annuity Business) (Details) - USD ($) $ in Thousands	3 Months Ended
Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016
Quarterly Financial Information Disclosure [Abstract]
Fixed index annuity derivatives, fair value accounting impact on comparability of net income (loss)	$ 3,518	$ 30,806	$ 37,075	$ 7,069	$ (66,618)	$ 6,054	$ 34,215	$ 62,822

Amount of the item included in the interim period that affected period-to-period comparability (excluding restatement adjustments).

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 270
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=84173487&loc=d3e1570-108306

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration