Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023
Statement Of Financial Position [Abstract]
Available-for-sale, amortized cost	$ 3,391,159	$ 3,054,391
Available-for-sale, allowance for credit losses	197	306
Equity securities, cost	417,897	354,022
Premiums and reinsurance balances receivable, allowances for uncollectible amounts	22,932	21,438
Reinsurance balances recoverable on unpaid losses and settlement expenses, allowances for uncollectible amounts	9,580	10,608
Property and equipment, accumulated depreciation	$ 76,330	$ 74,279
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized (in shares)	400,000,000	400,000,000
Common stock, shares issued (in shares)	137,598,560	137,140,522
Common stock, shares outstanding (in shares)	91,738,132	91,280,094
Treasury stock, shares (in shares)	45,860,428	45,860,428