Reinsurance - Effect of Reinsurance and Retrocessional Activity on Premiums Written and Earned and on Net Claims and Claim Expenses (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Premiums Written
Direct	$ 1,264,410	$ 994,286	$ 612,172
Assumed	7,949,130	6,839,512	5,193,993
Ceded	(2,017,380)	(1,894,423)	(1,709,832)
Net premiums written	7,196,160	5,939,375	4,096,333
Premiums Earned
Direct	1,105,164	799,717	536,595
Assumed	7,079,632	6,257,814	5,078,682
Ceded	(1,850,807)	(1,863,350)	(1,662,815)
Net premiums earned (Note 6)	6,333,989	5,194,181	3,952,462
Claims and Claim Expenses
Gross claims and claim expenses incurred	5,851,140	5,905,616	3,893,204
Claims and claim expenses recovered	(1,512,300)	(2,029,529)	(968,595)
Net claims and claim expenses incurred	$ 4,338,840	$ 3,876,087	$ 2,924,609