Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Statement of Financial Position [Abstract]
Interest bearing deposits, banks	$ 21,913	$ 10,978
Held-to-maturity securities, fair values	$ 1,076,790	$ 1,038,207
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	43,931,715	38,546,042
Common stock, shares outstanding	43,931,715	38,459,635
Treasury stock, shares	0	86,407