Equity (Accumulated Other Comprehensive Income (Loss)) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance			$ 428,612
Income tax benefit (expense)	$ (51,949)	$ (88,891)	(320,666)	$ (148,642)
Ending balance	1,634,932		1,634,932
Foreign Currency Translation Adjustment
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance			(934)	(1,078)
Change in OCI before reclassifications			(481)	(16)
Amounts reclassified from AOCI			0	0
Income tax benefit (expense)			101	3
Ending balance	(1,314)	(1,091)	(1,314)	(1,091)
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			1,563,347	698,743
Amounts reclassified from AOCI			(35,880)	9,087
Income tax benefit (expense)			(320,767)	(148,645)
Ending balance	1,636,246	235,890	1,636,246	235,890
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			1,562,866	698,727
Amounts reclassified from AOCI			(35,880)	9,087
Income tax benefit (expense)			(320,666)	(148,642)
Ending balance	1,634,932	234,799	1,634,932	234,799
Cash flow hedges | Net Unrealized Investment Gains (Losses)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance			0	(4,000)
Ending balance	$ 68,000	$ 0	$ 68,000	$ 0