Summary of Significant Accounting Policies - Deferred Policy Acquisition Costs (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Movement Analysis of Deferred Policy Acquisition Costs [Roll Forward]
Recorded asset at beginning of year	$ 87,094
Recorded asset at end of year	91,446	$ 87,094
Property and casualty business
Movement Analysis of Deferred Policy Acquisition Costs [Roll Forward]
Recorded asset at beginning of year	87,094	94,292	$ 92,796
Underwriting costs deferred	207,784	203,054	218,195
Amortization of deferred policy acquisition costs	(203,432)	(210,252)	(216,699)
Recorded asset at end of year	$ 91,446	$ 87,094	$ 94,292