Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Shareholders' equity:
Preferred stock, par value (in dollars per share)	$ 0.01	$ 0.01
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value (in dollars per share)	$ 2.50	$ 2.50
Common stock, shares authorized	80,000,000	40,000,000
Common stock, shares issued	36,759,656	24,230,392
Common stock, shares outstanding	36,759,656	24,230,392
Investment securities:
Securities held to maturity, fair value (in dollars)	$ 2,556	$ 6,250