Equity (Accumulated Other Comprehensive Income (Loss)) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance			$ 428,612
Income tax benefit (expense)	$ (7,006)	$ (132,024)	(327,672)	$ (280,666)
Ending balance	1,661,279		1,661,279
Foreign Currency Translation Adjustment
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance			(934)	(1,078)
Change in OCI before reclassifications			(154)	(244)
Amounts reclassified from AOCI			0	0
Income tax benefit (expense)			32	51
Ending balance	(1,056)	(1,271)	(1,056)	(1,271)
Net Unrealized Investment Gains (Losses)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance			429,546	(323,295)
Change in OCI before reclassifications			1,586,843	1,316,155
Amounts reclassified from AOCI			(26,350)	20,591
Income tax benefit (expense)			(327,704)	(280,717)
Ending balance	1,662,335	732,734	1,662,335	732,734
Accumulated Other Comprehensive Income (Loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance			428,612	(324,373)
Change in OCI before reclassifications			1,586,689	1,315,911
Amounts reclassified from AOCI			(26,350)	20,591
Income tax benefit (expense)			(327,672)	(280,666)
Ending balance	1,661,279	731,463	1,661,279	731,463
Cash flow hedges | Net Unrealized Investment Gains (Losses)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance			0	(4,000)
Ending balance	$ 23,000	$ 27,000	$ 23,000	$ 27,000