Premiums and Reinsurance Related Information (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021	Dec. 31, 2021	Dec. 31, 2020
Written premiums:
Written premiums, direct	$ 2,542,336	$ 2,177,162
Written premiums, assumed	317,500	307,550
Written premiums, ceded	(446,582)	(434,674)
Total net premiums written	2,413,254	2,050,038
Earned premiums:
Earned premiums, direct	2,404,597	2,003,045
Earned premiums, assumed	292,373	259,541
Earned premiums, ceded	(447,883)	(412,630)
Net premiums earned	2,249,087	1,849,956
Ceded losses and loss expenses incurred	243,294	298,740
Ceded commissions earned	117,445	101,680
Cumulative effect adjustment resulting from changes in accounting principles	$ 7,655	$ 7,373	$ 7,713	$ 7,801