CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Statement Of Financial Position [Abstract]
Held-to-maturity securities, fair value	$ 118,866	$ 118,955
Preferred stock, no par value
Preferred stock, shares authorized	1,000,000	1,000,000
Preferred stock, shares outstanding	0	0
Common stock, no par value
Common stock shares authorized	30,000,000	30,000,000
Common stock shares issued	14,574,339	14,538,085
Common stock shares outstanding	14,574,339	14,538,085