Earnings Per Share - Summary of Reconciliation Between Basic and Diluted Earnings Per Share (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Numerator:
Net income	$ 7,109	$ 7,676	$ 4,272	$ 6,198	$ 5,306	$ 6,659	$ 6,111	$ 5,805	$ 25,257	$ 23,881	$ 14,816
Less dividends and undistributed earnings allocated to participating securities									(210)	(239)	(157)
Net income applicable to common shareholders									$ 25,047	$ 23,642	$ 14,659
Denominator:
Weighted average number of shares outstanding, basic	4,939,973	4,815,020	4,682,109	4,072,805	4,065,681	4,064,620	4,059,927	4,053,355	4,629,255	4,061,529	4,030,530
Earnings per common share - basic	$ 1.43	$ 1.58	$ 0.91	$ 1.51	$ 1.29	$ 1.62	$ 1.49	$ 1.42	$ 5.41	$ 5.82	$ 3.64
Numerator:
Net income	$ 7,109	$ 7,676	$ 4,272	$ 6,198	$ 5,306	$ 6,659	$ 6,111	$ 5,805	$ 25,257	$ 23,881	$ 14,816
Less dividends and undistributed earnings allocated to participating securities									(210)	(239)	(157)
Net income applicable to common shareholders									$ 25,047	$ 23,642	$ 14,659
Denominator:
Weighted average number of shares outstanding, basic	4,939,973	4,815,020	4,682,109	4,072,805	4,065,681	4,064,620	4,059,927	4,053,355	4,629,255	4,061,529	4,030,530
Dilutive effect of common stock equivalents									33,000	37,000	35,000
Weighted average diluted common shares outstanding	4,980,439	4,842,965	4,715,724	4,106,658	4,102,546	4,101,378	4,094,489	4,071,975	4,661,720	4,098,633	4,065,754
Earnings per common share - diluted	$ 1.42	$ 1.57	$ 0.90	$ 1.49	$ 1.28	$ 1.61	$ 1.48	$ 1.41	$ 5.37	$ 5.77	$ 3.61