CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	Jun. 30, 2024	Dec. 31, 2023
Marketable securities, amortized cost	$ 4,636,825	$ 5,100,344
Held to maturity	$ 842,980	$ 838,241
Common stock, par value (in dollars per share)	$ 1	$ 1
Common stock, shares authorized (in shares)	60,000,000	60,000,000
Common stock, shares issued (in shares)	42,852,180	42,688,008
Preferred Stock
Preferred stock, par value (in dollars per share)	$ 1	$ 1
Preferred stock, shares authorized (in shares)	188,500	188,500
Preferred stock, shares issued (in shares)	0	0
Preferred stock, shares outstanding (in shares)	0	0
Series E Fixed-Rate Reset Cumulative Perpetual Preferred Stock
Preferred stock, par value (in dollars per share)	$ 1	$ 1
Preferred stock, shares authorized (in shares)	11,500	11,500
Preferred stock, shares issued (in shares)	11,500	11,500
Preferred stock, shares outstanding (in shares)	11,500	11,500
Significant Other Observable Inputs (Level 2)
Held to maturity	$ 809,516	$ 816,399
Obligations of states and political subdivisions
Held to maturity, allowance for credit losses	0	0
Held to maturity	$ 842,980	$ 838,241