Investments (Changes in Net Unrealized Gains/Losses on Investments) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Investment Holdings [Line Items]
Fixed maturity securities held for investment carried at amortized cost	$ 0	$ (1,445)	$ 0	$ (8,466)
Investments carried at fair value, fixed maturity securities, available for sale	1,383,290	(594,906)	2,900,810	(1,810,601)
Adjustment for effect on other balance sheet accounts:
Deferred policy acquisition costs and deferred sales inducements	(704,445)	316,964	(1,505,346)	960,287
Deferred income tax asset/liability	(142,558)	58,366	(293,048)	178,567
Total adjustment for effect on other balance sheet accounts	(847,003)	375,330	(1,798,394)	1,138,854
Change in net unrealized gains/losses on investments carried at fair value	536,287	(219,576)	1,102,416	(671,747)
Fixed Maturity Securities
Investment Holdings [Line Items]
Investments carried at fair value, fixed maturity securities, available for sale	$ 1,383,290	$ (594,906)	$ 2,900,810	$ (1,810,601)