CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Statement of Financial Position [Abstract]
Investment securities available-for-sale at amortized cost	$ 1,198,513	$ 966,900
Investment securities held-to-maturity	$ 35,942	$ 47,949
Common stock, par value (in dollars per share)	$ 1.00	$ 1.00
Common stock, shares authorized (in shares)	170,000,000	170,000,000
Common stock, shares issued (in shares)	82,334,257	83,265,674
Common stock, shares outstanding (in shares)	82,334,257	83,265,674