Condensed Consolidated Statements of Comprehensive Income (Loss) - Unaudited - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Statement Of Income And Comprehensive Income [Abstract]
Net income	$ 97,872	$ 72,469
Unrealized investment gains (losses) on available-for-sale securities:
Change in unrealized holding gains (losses) on available-for-sale securities	(64,890)	(86,887)
Reclassification adjustment for realized investment (gains) losses included in net income	(468)	3,410
Foreign currency translation adjustments:
Change in unrealized foreign currency translation gains (losses)	4,992	(29,011)
Total other comprehensive income (loss) before income taxes	(60,366)	(112,488)
Income tax expense (benefit) related to items of other comprehensive income (loss)	(14,283)	(17,596)
Other comprehensive income (loss), net of income taxes	(46,083)	(94,892)
Total comprehensive income (loss)	$ 51,789	$ (22,423)