Stock Option Plan - Schedule of Analysis of Stock Option Activity (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Outstanding, beginning of year, Shares	481,024
Granted, Shares
Exercised, Shares	(37,246)
Cancelled, Shares	(23,685)
Outstanding, end of year, Shares	420,093
Exercisable at end of year, Shares	179,678
Outstanding, beginning of year, Weighted-Average Ex. Price	$ 29.11
Granted, Weighted-Average Ex. Price
Exercised, Weighted-Average Ex. Price	$ 22.13
Cancelled, Weighted-Average Ex. Price	$ 31.95
Outstanding, end of year, Weighted-Average Ex. Price	$ 29.62
Exercisable at end of year, Weighted-Average Ex. Price	$ 26.75
Outstanding, end of year, Weighted-Average Remaining Contractual Term (Years)	6 years 22 days
Exercisable at end of year, Weighted-Average Remaining Contractual Term (Years)	3 years 11 months 1 day
Outstanding, end of year, Aggregate Intrinsic Value	$ 12,443
Exercisable at end of year, Aggregate Intrinsic Value	$ 4,806