Equity (Accumulated Other Comprehensive Income (Loss)) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	$ 428,612
Income tax benefit (expense)	(268,717)	$ (59,751)
Ending balance	1,439,500
Foreign Currency Translation Adjustment
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(934)	(1,078)
Change in OCI before reclassifications	(483)	100
Amounts reclassified from AOCI	0	0
Income tax benefit (expense)	102	(21)
Ending balance	(1,315)	(999)
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	1,309,567	282,844
Amounts reclassified from AOCI	(29,479)	1,584
Income tax benefit (expense)	(268,819)	(59,730)
Ending balance	1,440,815	(98,597)
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	1,309,084	282,944
Amounts reclassified from AOCI	(29,479)	1,584
Income tax benefit (expense)	(268,717)	(59,751)
Ending balance	1,439,500	(99,596)
Cash flow hedges | Net Unrealized Investment Gains (Losses)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	0	(4,000)
Ending balance	$ 103,000	$ (2,000)