Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Statement of Financial Position [Abstract]
Debt securities held to maturity, fair value	$ 268,803	$ 321,276
Loans held for sale, fair value	$ 18,935	$ 26,252
Common stock, par value (in dollars per share)	$ 1	$ 1
Common stock, authorized (in shares)	150,000,000	150,000,000
Common stock, issued (in shares)	79,234,077	77,579,561
Common stock, outstanding (in shares)	79,234,077	77,579,561
Common stock issuable (in shares)	674,499	607,869