Earnings Per Share - Summary of Reconciliation Between Basic and Diluted Earnings Per Share (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Numerator:
Net income	$ 4,272	$ 6,111	$ 10,470	$ 11,916
Less dividends and undistributed earnings allocated to participating securities	(35)	(60)	(94)	(121)
Net income applicable to common shareholders	$ 4,237	$ 6,051	$ 10,376	$ 11,795
Denominator:
Weighted average number of shares outstanding, basic	4,682,109	4,059,927	4,379,141	4,057,156
Earnings per common share - basic	$ 0.91	$ 1.49	$ 2.37	$ 2.91
Numerator:
Net income	$ 4,272	$ 6,111	$ 10,470	$ 11,916
Less dividends and undistributed earnings allocated to participating securities	(35)	(60)	(94)	(121)
Net income applicable to common shareholders	$ 4,237	$ 6,051	$ 10,376	$ 11,795
Denominator:
Weighted average number of shares outstanding, basic	4,682,109	4,059,927	4,379,141	4,057,156
Dilutive effect of common stock equivalents	34,000	34,000	33,000	31,000
Weighted average diluted common shares outstanding	4,715,724	4,094,489	4,412,239	4,087,790
Earnings per common share - diluted	$ 0.90	$ 1.48	$ 2.35	$ 2.89