Other Comprehensive Income - Components of accumulated other comprehensive income (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	$ (64,600)	$ 488,895	$ 212,091
Other comprehensive income (loss) before reclassifications	(1,829,369)	(437,427)	702,991
Amounts reclassified from accumulated other comprehensive income	247,799	(116,068)	(426,187)
Net current period other comprehensive income (loss)	(1,581,570)	(553,495)	276,804
Ending balance	(1,646,170)	(64,600)	488,895
Unrealized Appreciation on Available-For-Sale Investments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	13,486	501,295	258,486
Other comprehensive income (loss) before reclassifications	(1,772,649)	(371,741)	668,996
Amounts reclassified from accumulated other comprehensive income	247,799	(116,068)	(426,187)
Net current period other comprehensive income (loss)	(1,524,850)	(487,809)	242,809
Ending balance	(1,511,364)	13,486	501,295
Foreign Currency Translation Adjustments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(78,086)	(12,400)	(46,395)
Other comprehensive income (loss) before reclassifications	(56,720)	(65,686)	33,995
Amounts reclassified from accumulated other comprehensive income	0	0	0
Net current period other comprehensive income (loss)	(56,720)	(65,686)	33,995
Ending balance	$ (134,806)	$ (78,086)	$ (12,400)