CONSOLIDATED BALANCE SHEETS (UNAUDITED) (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
AVAILABLE FOR SALE
Securities available for sale, amortized cost	$ 2,500,696	$ 2,306,741
Held-to-maturity Securities, Other Disclosure Items [Abstract]
Securities held to maturity, fair value	$ 125,381	$ 138,879
Shareholders' equity:
Common stock, par value (in dollars per share)	$ 1.25	$ 1.25
Common stock, shares authorized (in shares)	80,000,000	80,000,000
Common stock, shares issued (in shares)	37,922,002	37,887,662
Treasury stock (in shares)	4,849,881	4,064,405