Earnings per Share - Basic and Diluted Earnings Per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Earnings Per Share, Basic and Diluted [Abstract]
Net income	$ 7,158	$ 7,528	$ 6,466	$ 6,116	$ 5,190	$ 6,235	$ 5,080	$ 5,726	$ 27,268	$ 22,231	$ 21,189
Net income allocated to unvested restricted stock									(204)	(245)	(237)
Net income allocated to common shares									$ 27,064	$ 21,986	$ 20,952
Denominator for basic earnings per share—weighted-average shares outstanding									19,491	16,056	16,420
Effect of dilutive securities—employee stock options									31	23	6
Denominator for diluted earnings per share—adjusted weighted-average shares outstanding									19,522	16,079	16,426
Basic earnings per share	$ 0.37	$ 0.39	$ 0.33	$ 0.31	$ 0.32	$ 0.38	$ 0.31	$ 0.35	$ 1.39	$ 1.37	$ 1.28
Diluted earnings per share	$ 0.37	$ 0.39	$ 0.33	$ 0.31	$ 0.32	$ 0.38	$ 0.31	$ 0.35	$ 1.39	$ 1.37	$ 1.28
Average anti-dilutive options and awards excluded from computation of diluted earnings per share									558	559	600