Earnings and Dividends per Share - Number of Shares Outstanding for Calculation of Earnings Per Share (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Earnings Per Share [Abstract]
Basic net income and earnings per share, Numerator (Income)	$ 5,486	$ 4,050	$ 5,524	$ 7,150
Diluted earnings and earnings per share, Numerator (Income)	$ 5,486	$ 4,050	$ 5,524	$ 7,150
Basic net income and earnings per share, Denominator (Shares)	34,473,688	33,946,117	34,345,317	33,937,128
Common stock equivalents arising from stock options, restricted stock awards, and employee stock purchase plan, Denominator (Shares)	333,000	216,000	341,000	202,000
Diluted earnings and earnings per share, Denominator (Shares)	34,806,808	34,161,543	34,685,687	34,139,087
Basic net income and earnings per share, Per Share Amount	$ 0.16	$ 0.12	$ 0.16	$ 0.21
Diluted earnings and earnings per share, Per Share Amount	$ 0.16	$ 0.12	$ 0.16	$ 0.21