Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2026	Dec. 31, 2025
Statement of Financial Position [Abstract]
Available-for-sale, amortized cost	$ 3,669,921	$ 3,642,362
Available-for-sale, allowance for credit losses	538	828
Equity securities, cost	539,859	534,311
Premiums and reinsurance balances receivable, allowances for uncollectible amounts	21,696	23,673
Reinsurance balances recoverable on unpaid losses and settlement expenses, allowances for uncollectible amounts	11,479	11,107
Property and equipment, accumulated depreciation	$ 86,547	$ 84,459
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)	137,794,359	137,739,079
Common stock, shares outstanding (in shares)	91,933,931	91,878,651
Treasury stock, shares (in shares)	45,860,428	45,860,428