Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017
Investment securities:
Securities held to maturity, fair value (in dollars)	$ 1,284	$ 2,556	$ 6,217
Shareholders' equity:
Preferred stock, par value (in dollars per share)	$ 0.01	$ 0.01	$ 0.01
Preferred stock, shares authorized	10,000,000	10,000,000	10,000,000
Preferred stock, shares issued	0	0	0
Preferred stock, shares outstanding	0	0	0
Common stock, par value (in dollars per share)	$ 2.50	$ 2.50	$ 2.50
Common stock, shares authorized	80,000,000	80,000,000	40,000,000
Common stock, shares issued	36,783,438	36,759,656	29,230,734
Common stock, shares outstanding	36,783,438	36,759,656	29,230,734