Earnings Per Share - Computation of Earnings Per Share (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended							9 Months Ended
	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Sep. 30, 2014	Sep. 30, 2013
Earnings Per Share [Abstract]
Net income	$ 8,234	$ 4,859	$ 7,365	$ 5,236	$ 7,361	$ 6,325	$ 8,477	$ 20,458	$ 22,163
Average number of common shares outstanding	16,137				16,074			16,121	16,035
Effect of dilutive stock options and restricted stock units	194				156			200	117
Average number of common shares outstanding used to calculate diluted earnings per share	16,331				16,230			16,321	16,152
Options excluded from diluted earnings per share because the effect of these options was antidilutive	127				171			110	544