Reserve for Losses and Loss Adjustment Expenses - Reconciliation of beginning and ending balances of losses and loss adjustment reserves (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Liability for Future Policy Benefits and Unpaid Claims and Claims Adjustment Expense [Abstract]
Reserve for losses and loss adjustment expenses at beginning of period		$ 18,194,324	$ 17,196,648	$ 17,757,156	$ 16,513,929
Unpaid losses and loss adjustment expenses recoverable		5,686,348	4,146,020	5,599,231	4,314,855
Net reserve for losses and loss adjustment expenses at beginning of period		12,507,976	13,050,628	12,157,925	12,199,074
Net incurred losses and loss adjustment expenses relating to losses occurring in:
Current year		1,863,519	1,348,528	4,280,048	3,812,381
Prior years		(180,823)	(122,509)	(493,861)	(223,431)
Total net incurred losses and loss adjustment expenses		1,682,696	1,226,019	3,786,187	3,588,950
Net losses and loss adjustment expense reserves of acquired business	[1]	0	104,307	0	104,307
Retroactive reinsurance transaction	[2]	0	0	0	(183,893)
Impact of deconsolidation of Somers		0	(1,460,611)	0	(1,460,611)
Net foreign exchange (gains) losses and other		(243,387)	(78,152)	(524,682)	10,818
Net paid losses and loss adjustment expenses relating to losses occurring in:
Current year		(226,575)	(208,923)	(463,847)	(432,348)
Prior years		(538,967)	(417,368)	(1,773,840)	(1,610,397)
Total net paid losses and loss adjustment expenses		(765,542)	(626,291)	(2,237,687)	(2,042,745)
Net reserve for losses and loss adjustment expenses at end of period		13,181,743	12,215,900	13,181,743	12,215,900
Unpaid losses and loss adjustment expenses recoverable		6,106,548	5,115,147	6,106,548	5,115,147
Reserve for losses and loss adjustment expenses at end of period		$ 19,288,291	$ 17,331,047	$ 19,288,291	$ 17,331,047

[1] Represents activity related to the Company’s acquisitions in the 2021 period of the Westpac Lenders Mortgage Insurance Limited and Somerset Bridge Group Limited, Southern Rock Holdings Limited and affiliates.

[2] During the 2021 first quarter, the Company entered into a reinsurance to close and other related agreements with Premia Managing Agency Limited (“Premia”), in connection with the 2018 and prior years of account related to the acquisition of Barbican Group Holdings Limited (“Barbican”).