Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2025	Dec. 31, 2024
Statement Of Financial Position [Abstract]
Available-for-sale, amortized cost	$ 3,448,746	$ 3,391,159
Available-for-sale, allowance for credit losses	157	197
Equity securities, cost	447,799	417,897
Premiums and reinsurance balances receivable, allowances for uncollectible amounts	23,085	22,932
Reinsurance balances recoverable on unpaid losses and settlement expenses, allowances for uncollectible amounts	10,341	9,580
Property and equipment, accumulated depreciation	$ 78,322	$ 76,330
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)	137,633,162	137,598,560
Common stock, shares outstanding (in shares)	91,772,734	91,738,132
Treasury stock, shares (in shares)	45,860,428	45,860,428