Other Comprehensive Income - Amounts reclassified from accumulated other comprehensive income (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Provision for credit losses	$ (2,100)	$ (3,597)	$ 0
Other-than-temporary impairment losses	0	(533)
Other-than-temporary Impairment Loss, Debt Securities, Available-for-sale, Recognized in Earnings			(3,165)
Income (loss) before income taxes	2,368,042	1,577,549	1,849,110
Income tax (expense) benefit	(128,582)	(111,838)	(155,810)
Net of tax	2,156,849	1,405,521	1,636,319
Reclassification out of accumulated other comprehensive income | Unrealized Appreciation on Available-For-Sale Investments
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Net realized gains (losses)	157,095	478,659	131,043
Provision for credit losses	(2,099)	(3,597)	0
Other-than-temporary impairment losses	0	(533)
Other-than-temporary Impairment Loss, Debt Securities, Available-for-sale, Recognized in Earnings			(3,165)
Income (loss) before income taxes	154,996	474,529	127,878
Income tax (expense) benefit	(38,928)	(48,342)	(8,937)
Net of tax	$ 116,068	$ 426,187	$ 118,941