Schedule IV - Reinsurance (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2022	Dec. 31, 2021		Dec. 31, 2020
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Gross Amount		$ 8,540,787	$ 7,706,832		$ 6,553,910
Ceded to other Companies		(4,249,258)	(3,734,150)		(2,650,352)
Assumed From Other Companies		6,785,660	5,045,655		3,534,158
Net Amount		$ 11,077,189	$ 9,018,337		$ 7,437,716
Percentage of Amount Assumed to Net		61.30%	55.90%		47.50%
Operating segments | Insurance
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Gross Amount		$ 6,889,358	$ 5,833,873		$ 4,659,416
Ceded to other Companies	[1]	(1,910,222)	(1,719,541)		(1,525,655)
Assumed From Other Companies	[1]	41,506	33,861		29,146
Net Amount		$ 5,020,642	$ 4,148,193		$ 3,162,907
Percentage of Amount Assumed to Net		0.80%	0.80%		0.90%
Operating segments | Reinsurance
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Gross Amount		$ 395,063	$ 408,520		$ 305,435
Ceded to other Companies	[1]	(2,024,462)	(1,839,556)		(1,014,716)
Assumed From Other Companies	[1]	6,553,375	4,685,410		3,166,651
Net Amount		$ 4,923,976	$ 3,254,374		$ 2,457,370
Percentage of Amount Assumed to Net		133.10%	144.00%		128.90%
Operating segments | Mortgage
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Gross Amount		$ 1,256,366	$ 1,213,333		$ 1,192,316
Ceded to other Companies	[1]	(322,400)	(246,757)		(194,149)
Assumed From Other Companies	[1]	198,605	294,492		281,683
Net Amount		$ 1,132,571	$ 1,261,068		$ 1,279,850
Percentage of Amount Assumed to Net		17.50%	23.40%		22.00%
Operating segments | Other
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Gross Amount			$ 251,106		$ 396,743
Ceded to other Companies		$ 0	(102,763)	[1]	(190,957)	[1]
Assumed From Other Companies	[1]		206,359		331,803
Net Amount		$ 0	$ 354,702		$ 537,589
Percentage of Amount Assumed to Net			58.20%		61.70%

[1] Certain amounts included in the gross premiums written of each segment are related to intersegment transactions and are included in the gross premiums written of each segment. Accordingly, the sum of gross premiums written for each segment does not agree to the total gross premiums written as shown in the table above due to the elimination of intersegment transactions in the total.