Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Statement of Financial Position [Abstract]
Fixed income securities, held-to-maturity, fair value	$ 21,923	$ 29,837
Fixed income securities, available-for-sale, allowance for credit loss	28,212	45,721
Fixed income securities, available-for-sale, amortized cost	7,880,697	7,185,754
Commercial mortgage loans, fair value	178,913	139,243
Equity securities, at cost	183,076	167,431
Accumulated depreciation and amortization, property and equipment	$ 271,409	$ 251,209
Preferred Stock, Par or Stated Value (in dollars per share)	$ 0	$ 0
Preferred Stock, Shares Authorized	5,000,000	5,000,000
Preferred Stock, Shares Issued	8,000	8,000
Preferred Stock, Shares Outstanding	8,000	8,000
Common Stock, Par or Stated Value (in dollars per share)	$ 2	$ 2
Common Stock, Shares Authorized	360,000,000	360,000,000
Common Stock, Shares, Issued	105,223,307	104,847,111
Treasury Stock, Shares	44,586,870	44,508,211