Equity (Accumulated Other Comprehensive Income (Loss)) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jan. 01, 2019	[1]	Jan. 01, 2018
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning Balance	$ (324,373)
Income tax benefit (expense)	291,101	$ (161,504)	$ (1,201,099)
Cumulative effect of adoption		42
Ending Balance	428,612	(324,373)
Foreign Currency Translation Adjustment
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning Balance	(1,078)	(7)	(78)
Change in OCI before reclassifications	182	(1,354)	109
Amounts reclassified from AOCI	0	0	0
Income tax benefit (expense)	(38)	285	(38)
Ending Balance	(934)	(1,078)	(7)
Net Unrealized Investment Gains (Losses)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning Balance	(323,295)	(90,117)	(314,870)
Change in OCI before reclassifications	956,373	(311,658)	320,182
Amounts reclassified from AOCI	(3,123)	62,970	3,177
Income tax benefit (expense)	(200,409)	52,225	(98,606)
Ending Balance	429,546	(323,295)	(90,117)
Total Accumulated Other Comprehensive Income (Loss)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning Balance	(324,373)	(90,124)	(314,948)
Change in OCI before reclassifications	956,555	(313,012)	320,291
Amounts reclassified from AOCI	(3,123)	62,970	3,177
Income tax benefit (expense)	(200,447)	52,510	(98,644)
Cumulative effect of adoption				$ 0		$ (36,700)
Ending Balance	428,612	(324,373)	(90,124)
ASU 2016-01 | Foreign Currency Translation Adjustment
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Cumulative effect of adoption		0
ASU 2016-01 | Net Unrealized Investment Gains (Losses)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Cumulative effect of adoption		(3)
ASU 2016-01 | Total Accumulated Other Comprehensive Income (Loss)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Cumulative effect of adoption		(3)				$ (3)
ASU 2018-02 | Foreign Currency Translation Adjustment
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Cumulative effect of adoption		(2)
ASU 2018-02 | Net Unrealized Investment Gains (Losses)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Cumulative effect of adoption		(36,712)
ASU 2018-02 | Total Accumulated Other Comprehensive Income (Loss)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Cumulative effect of adoption		(36,714)
Cash flow hedges | Net Unrealized Investment Gains (Losses)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning Balance	(4,000)	(26,000)
Ending Balance	$ 0	$ (4,000)	$ (26,000)

[1] Includes the impact from the adoption of ASUs 2017-08 and 2017-12. See Note 2.