Consolidated Balance Sheets (Parenthetical) - USD ($)	Dec. 31, 2020	Dec. 31, 2019
Statement Of Financial Position [Abstract]
Interest bearing deposits, banks	$ 721,086,000	$ 51,891,000
Held-to-maturity securities, fair values	$ 768,183,000	$ 874,523,000
Preferred stock, no par value
Preferred stock, shares authorized	1,000,000	1,000,000
Preferred stock, shares issued	150,000	0
Preferred stock, shares outstanding	150,000	0
6.75% non-cumulative perpetual preferred stock, Series A, liquidation preference	$ 150,000,000
Common stock, par value	$ 2.0833	$ 2.0833
Common stock, shares authorized	100,000,000	100,000,000
Common stock, shares issued	68,081,306	68,078,116
Common stock, shares outstanding	67,254,706	67,824,428
Treasury stock, shares	826,600	253,688