Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Statement of Comprehensive Income [Abstract]
Net income	$ 600,671	$ 393,626	$ 672,309
Other comprehensive income (loss), net of tax (Note 15)
Unrealized holding gains (losses) on investments arising during the period for which an allowance for expected losses has not been recognized	(138,435)	178,761	180,441
Less: Reclassification adjustment for net gains (losses) on investments included in net income
Net realized gains on disposals and non-credit related impairment losses	4,472	26,440	8,897
Net decrease (increase) in expected credit losses	725	(991)	0
Net unrealized gains (losses) on investments	(143,632)	153,312	171,544
Other adjustments to comprehensive income, net	0	(75)	(136)
Other comprehensive income (loss), net of tax	(143,632)	153,237	171,408
Comprehensive income	$ 457,039	$ 546,863	$ 843,717