Consolidated Balance Sheets (Parentheticals) - USD ($) $ in Thousands	Jun. 30, 2024	Dec. 31, 2023
Statement of Financial Position [Abstract]
Fixed income securities, held-to-maturity, fair value	$ 18,556	$ 21,923
Fixed income securities, available-for-sale, allowance for credit loss	31,309	28,212
Fixed income securities, available-for-sale, amortized cost	8,080,498	7,880,697
Commercial mortgage loans, fair value	209,041	178,913
Equity securities, cost	187,286	183,076
Property and equipment, accumulated depreciation and amortization	$ 278,525	$ 271,409
Preferred stock, par or stated value (in dollars per share)	$ 0	$ 0
Preferred stock, authorized (in shares)	5,000,000	5,000,000
Preferred stock, issued (in shares)	8,000	8,000
Preferred stock, liquidation preference (in dollars per share)	$ 25,000	$ 25,000
Common stock, par or stated value (in dollars per share)	$ 2	$ 2
Common stock, authorized (in shares)	360,000,000	360,000,000
Common stock, issued (in shares)	105,516,194	105,223,307
Treasury stock, common (in shares)	44,656,246	44,586,870