Earnings Per Share - Computation of Earnings Per Share (Detail) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended							9 Months Ended
	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Sep. 30, 2016	Sep. 30, 2015
Earnings Per Share [Abstract]
Net income	$ 12,199	$ 9,405	$ 10,674	$ 11,422	$ 12,694	$ 11,366	$ 8,336	$ 32,278	$ 32,396
Average number of common shares outstanding	22,825				22,757			22,804	22,743
Effect of dilutive stock options and restricted stock units	274				249			273	236
Average number of common shares outstanding used to calculate diluted earnings per share	23,099				23,006			23,077	22,979
Options excluded from diluted earnings per share because the effect of these options was antidilutive	12				23			18	23