Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Statement Of Financial Position [Abstract]
Investment securities held-to-maturity, fair value	$ 128,352	$ 100,483
Common Stock, Par Value	$ 1.00	$ 1.00
Common Stock, Shares Authorized	10,000,000	10,000,000
Common Stock, Shares, Issued	6,122,717	4,242,216
Common Stock, Shares, Outstanding	6,122,717	4,242,216