CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) shares in Thousands, $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Statement of Financial Position [Abstract]
Fixed maturities, available for sale, amortized cost	$ 12,241,782	$ 11,566,930
Allowance for expected credit losses on fixed maturities, available for sale	313	323
Fixed maturities, held to maturity, fair value	445,033	0
Fixed maturities, held to maturity, allowance for credit loss	0
Equity securities, cost	528,864	421,744
Credit losses associated with commercial mortgage loans	0	0
Allowance for credit losses on premium balances receivable	7,567	8,836
Allowance for credit losses on reinsurance recoverable for unpaid losses and loss expenses	$ 29,554	$ 23,711
Common shares, shares issued (in shares)	176,580	176,580
Common shares, shares outstanding (in shares)	84,774	84,353
Treasury shares (in shares)	91,806	92,227

The reserve to cover probable credit losses related to specifically identified fixed maturity real estate loans as well as probable credit losses inherent in the remainder of that loan portfolio.

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