Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Statement of Financial Position [Abstract]
Securities available for sale, amortized cost	$ 2,103,362	$ 1,900,684
Securities held to maturity	19,708	20,018
Loans held for sale at fair value	$ 282,439	$ 263,308
Preferred stock, par value	$ 1.00	$ 1.00
Preferred stock, shares authorized	50,000,000	50,000,000
Preferred stock, shares issued	0	0
Common stock, par value	$ 2.50	$ 2.50
Common stock, shares authorized	200,000,000	200,000,000
Common stock, shares issued	105,208,914	105,069,821
Common stock, shares in treasury	1,005,372	29,173