Net Income Per Share - Computation of Basic and Diluted Net Income Per Share (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Numerator:
Net income	$ 5,761	$ 22,768
Denominator:
Shares used in net income per common share - basic	52,773,000	52,504,000
Effect of dilutive securities:
Stock options, restricted stock and employee stock purchase plan	586,000	718,000
Shares used in net income per common share - diluted	53,359,000	53,222,000
Net income per common share:
Basic	$ 0.11	$ 0.43
Diluted	$ 0.11	$ 0.43