Schedule III - Supplementary Insurance Information (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]
Deferred Acquisition Costs		$ 1,263,870	$ 901,841	$ 790,708
Reserves for Losses and Loss Adjustment Expenses		20,031,943	17,757,156	16,513,928
Unearned Premiums		7,337,002	6,011,942	4,838,965
Net Premiums Earned		9,678,077	8,082,298	6,991,935
Net Losses and Loss Adjustment Expenses Incurred		5,027,517	4,584,803	4,689,599
Amortization of Deferred Acquisition Costs		1,739,580	1,303,178	1,004,842
Other Operating Expenses	[1]	1,128,175	998,595	875,176
Net Premiums Written		11,077,189	9,018,337	7,437,716
Operating segments | Insurance
SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]
Deferred Acquisition Costs		301,398	378,265	254,833
Reserves for Losses and Loss Adjustment Expenses		11,017,327	9,810,622	8,989,930
Unearned Premiums		3,381,810	2,937,664	2,334,225
Net Premiums Earned		4,559,335	3,626,468	2,871,420
Net Losses and Loss Adjustment Expenses Incurred		2,782,945	2,344,365	2,092,453
Amortization of Deferred Acquisition Costs		885,866	606,265	418,483
Other Operating Expenses	[1]	665,472	558,906	489,153
Net Premiums Written		5,020,642	4,148,193	3,162,907
Operating segments | Reinsurance
SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]
Deferred Acquisition Costs		992,339	424,390	278,422
Reserves for Losses and Loss Adjustment Expenses		8,305,854	6,878,721	5,027,742
Unearned Premiums		3,206,284	2,263,264	1,356,983
Net Premiums Earned		3,959,381	2,840,443	2,162,229
Net Losses and Loss Adjustment Expenses Incurred		2,568,843	1,924,719	1,628,320
Amortization of Deferred Acquisition Costs		813,555	536,754	354,048
Other Operating Expenses	[1]	267,531	212,810	168,011
Net Premiums Written		4,923,976	3,254,374	2,457,370
Operating segments | Mortgage
SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]
Deferred Acquisition Costs		(29,867)	99,186	203,748
Reserves for Losses and Loss Adjustment Expenses		708,762	1,067,813	976,673
Unearned Premiums		748,908	811,014	740,043
Net Premiums Earned		1,159,361	1,283,419	1,397,935
Net Losses and Loss Adjustment Expenses Incurred		(324,271)	56,677	528,344
Amortization of Deferred Acquisition Costs		40,159	97,418	134,240
Other Operating Expenses	[1]	195,172	194,010	162,202
Net Premiums Written		1,132,571	1,261,068	1,279,850
Operating segments | Other
SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]
Deferred Acquisition Costs				53,705
Reserves for Losses and Loss Adjustment Expenses				1,519,583
Unearned Premiums				407,714
Net Premiums Earned			331,968	560,351
Net Losses and Loss Adjustment Expenses Incurred			259,042	440,482
Amortization of Deferred Acquisition Costs			62,741	98,071
Other Operating Expenses	[1]		32,869	55,810
Net Premiums Written			$ 354,702	$ 537,589

[1] Certain other operating expenses relate to the Company’s corporate segment. Such amounts are not reflected in the table above. See note 4, “Segment Information,” to our consolidated financial statements in Item 8 for information related to the corporate segment.