Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018
Investment securities:
Securities held to maturity, fair value (in dollars)	$ 0	$ 1,284
Shareholders' equity:
Common stock, par value (in dollars per share)	$ 2.50	$ 2.50	$ 2.50
Common stock, shares authorized	80,000,000	80,000,000	80,000,000
Common stock, shares issued	35,368,521	35,829,549	36,783,438
Common stock, shares outstanding	35,368,521	35,829,549	36,783,438