Stock Option Activity (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Option shares
Options Outstanding at beginning of period	236,404
Granted	32,768
Exercised	(43,463)	(4,323)	(3,854)
Canceled	(25,313)
Options Outstanding at end of period	200,396	236,404
Options Exercisable at end of period	167,628
Weighted average exercise price per share
Options Outstanding at beginning of period	$ 20.17
Granted	20.15
Exercised	17.26
Canceled	28.56
Options Outstanding at end of period	19.73	$ 20.17
Options Exercisable at end of period	$ 19.65
Weighted average remaining contractual term (years)
Options Outstanding at end of period	6 years 1 month 6 days
Options Exercisable at end of period	5 years 6 months
Aggregate Intrinsic Value
Options Outstanding at end of period	$ 2,123
Options Exercisable at end of period	$ 1,790