Equity - Reclassifications out of 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
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Investment fair value changes, net	$ 152,228	$ 3,138	$ (718,604)	$ 23,297
Realized gains, net	(25,965)	(2,827)	(29,817)	(13,513)
Net income before provision for income taxes	165,481	33,599	(800,146)	88,946
Reclassification out of Accumulated Other Comprehensive Income | Net Unrealized Gains (Losses) on Available-for-Sale Securities
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Investment fair value changes, net	(54)	0	1,471	0
Realized gains, net	2,772	(2,822)	(12,551)	(12,315)
Net income before provision for income taxes	$ 2,718	$ (2,822)	$ (11,080)	$ (12,315)