CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) shares in Thousands, $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Statement of Financial Position [Abstract]
Amortized cost	$ 12,587,327	$ 12,176,473
Fixed maturities, available for sale, allowance for credit loss	8,933	11,733
Fixed maturities, held to maturity, fair value	696,639	674,743
Fixed maturities, held to maturity, allowance for credit loss	0	0
Equity securities, cost	561,558	494,356
Mortgage loans, held for investment, allowance for credit loss	4,179	0
Allowance for expected credit losses on insurance and reinsurance premium balances receivable	14,781	9,521
Allowance for expected credit losses on reinsurance recoverable for unpaid losses and loss expenses	$ 34,724	$ 30,715
Common shares, shares issued (in shares)	176,580	176,580
Common shares, shares outstanding (in shares)	85,228	84,668
Treasury shares, shares (in shares)	91,352	91,912