Consolidated Balance Sheets (Parenthetical) - USD ($)	Jun. 30, 2021	Dec. 31, 2020
Statement Of Financial Position [Abstract]
Interest bearing deposits, banks	$ 637,312,000	$ 721,086,000
Held-to-maturity securities, fair values	$ 934,487,000	$ 768,183,000
Preferred stock, no par value
Preferred stock, shares authorized	1,000,000	1,000,000
Preferred stock, shares issued	150,000	150,000
Preferred stock, shares outstanding	150,000	150,000
6.75% non-cumulative perpetual preferred stock, Series A, liquidation preference	$ 150,000,000	$ 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	68,081,306
Common stock, shares outstanding	65,970,149	67,254,706
Treasury stock, shares	2,111,157	826,600