Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Statement Of Financial Position [Abstract]
Interest bearing deposits, banks	$ 51,891	$ 44,536
Held-to-maturity securities, fair values	$ 874,523	$ 1,020,743
Preferred stock, no par value
Preferred stock, shares authorized	1,000,000	1,000,000
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 2.0833	$ 2.0833
Common stock, shares authorized	100,000,000	100,000,000
Common stock, shares issued	68,078,116	54,604,294
Common stock, shares outstanding	67,824,428	54,598,134
Treasury stock, shares	253,688	6,160