Reinsurance - Effects of reinsurance (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Premiums Written
Direct	$ 8,540,787	$ 7,706,832	$ 6,553,910
Assumed	6,785,660	5,045,655	3,534,158
Ceded	(4,249,258)	(3,734,150)	(2,650,352)
Net premiums written	11,077,189	9,018,337	7,437,716
Premiums Earned
Direct	8,057,635	7,149,794	6,361,451
Assumed	5,767,738	4,333,873	3,213,873
Ceded	(4,147,296)	(3,401,369)	(2,583,389)
Net premiums earned	9,678,077	8,082,298	6,991,935
Losses and Loss Adjustment Expenses
Direct	3,990,768	4,266,758	4,392,392
Assumed	3,559,133	2,826,820	2,204,323
Ceded	(2,522,384)	(2,508,775)	(1,907,116)
Net	$ 5,027,517	$ 4,584,803	$ 4,689,599