Other Comprehensive Income - Amounts reclassified from accumulated other comprehensive income (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Provision for credit losses	$ (43,909)	$ (2,100)	$ (3,597)
Other-than-temporary impairment losses	0	0
Other-than-temporary impairment losses			(533)
Income (loss) before income taxes	1,562,384	2,368,042	1,577,549
Income tax (expense) benefit	(79,961)	(128,582)	(111,838)
Net of tax	1,476,933	2,156,849	1,405,521
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)	(235,989)	157,095	478,659
Provision for credit losses	(43,909)	(2,099)	(3,597)
Other-than-temporary impairment losses	0	0
Other-than-temporary impairment losses			(533)
Income (loss) before income taxes	(279,898)	154,996	474,529
Income tax (expense) benefit	32,099	(38,928)	(48,342)
Net of tax	$ (247,799)	$ 116,068	$ 426,187