Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022
Investment securities:
Securities held to maturity, fair value (in dollars)	$ 2,227,612	$ 2,250,168
Shareholders' equity:
Common stock, par value (in dollars per share)	$ 2.50	$ 2.50
Common stock, shares authorized	160,000,000	160,000,000
Common stock, shares issued	75,859,665	75,704,563
Common stock, shares outstanding	75,859,665	75,704,563