Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Statement Of Financial Position [Abstract]
Investment securities held-to-maturity, fair value	$ 170,399	$ 137,476
Common Stock, Par Value	$ 1.00	$ 1.00
Common Stock, Shares Authorized	20,000,000	20,000,000
Common Stock, Shares, Issued	8,484,328	8,480,938
Common Stock, Shares, Outstanding	8,484,328	8,480,938