Stock-Based Compensation - Employee Stock Purchase Plan - Additional Information (Detail) (Employee Stock Purchase Plan [Member], USD $)	12 Months Ended
	Dec. 31, 2014 H	Aug. 31, 2014	Jul. 31, 2014	Dec. 31, 2013	Aug. 31, 2013	Jul. 31, 2013	Dec. 31, 2012	Aug. 31, 2012	Jul. 31, 2012
Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available for issuance or authorized shares				12,000,000
Shares available for future grants or for future subscription	734,317
Number of hours worked per week by employees	20
Maximum percentage of allotment through payroll deductions	10.00%
Allotted value, maximum, to purchase Company stock	$ 25,000
Subscription Period, beginning	August 1
Subscription Period, ending	July 31
Stock price, percentage	85.00%
Quoted market price of Company's stock	15.00%
Value of a one-year stock option, percentage	85.00%
Fair value of an ESPP share option		$ 6.39			$ 8.36			$ 5.84
Issued shares of common stock			512,521			487,672			562,748
Aggregate purchase price of issued common stock	13,408,000			10,456,000			9,302,000
Aggregate purchase price per share of issued common stock	$ 26.16			$ 21.44			$ 16.53
Shares of common stock subscribed	235,794			222,526			246,164
Proceeds by participants	$ 6,277,000			$ 5,937,000			$ 5,278,000