Accounting Policies - Narrative (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2022 USD ($) reinsurance_company insurance_company	Mar. 31, 2021 USD ($)	Dec. 31, 2021 USD ($)
Accounting Policies [Line Items]
Investment in variable interest entities	$ 28,500		$ 26,900
Pre-tax income (loss)	13,528	$ (140,829)
Income tax expense (benefit)	3,323	(37,369)
Development on prior year loss reserves	$ 6,804	$ 170,134
Effective U.S. federal income tax expense (benefit) rate	24.60%	(26.50%)
Excess and Surplus Lines
Accounting Policies [Line Items]
Development on prior year loss reserves	$ (59)	$ 168,700
UNITED STATES
Accounting Policies [Line Items]
Number of insurance companies | insurance_company	5
BERMUDA
Accounting Policies [Line Items]
Number of insurance companies | reinsurance_company	2