Equity (Accumulated Other Comprehensive Income (Loss)) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	$ 1,533,059
Income tax benefit (expense)	375,580	$ (268,717)
Ending balance	120,164
Foreign Currency Translation Adjustment
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(708)	(934)
Change in OCI before reclassifications	49	(483)
Amounts reclassified from AOCI	0	0
Income tax benefit (expense)	(10)	102
Ending balance	(669)	(1,315)
Net Unrealized Investment Gains (Losses)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	1,533,767	429,546
Change in OCI before reclassifications	(694,704)	1,309,567
Amounts reclassified from AOCI	(1,093,820)	(29,479)
Income tax benefit (expense)	375,590	(268,819)
Ending balance	120,833	1,440,815
Accumulated Other Comprehensive Income (Loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	1,533,059	428,612
Change in OCI before reclassifications	(694,655)	1,309,084
Amounts reclassified from AOCI	(1,093,820)	(29,479)
Income tax benefit (expense)	375,580	(268,717)
Ending balance	120,164	1,439,500
Cash flow hedges | Net Unrealized Investment Gains (Losses)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(43,000)	0
Ending balance	$ (40,000)	$ 103,000