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		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Numerator:
Net income	$ 29,117	$ 2,458	$ 81,586	$ 15,539
Denominator:
Shares used in net income per common share - basic	53,054,000	53,165,000	53,276,000	52,998,000
Effect of dilutive securities:
Stock options, restricted stock and employee stock purchase plan	256,000	348,000	265,000	412,000
Shares used in net income per common share - diluted	53,310,000	53,513,000	53,541,000	53,410,000
Net income per common share:
Basic	$ 0.55	$ 0.05	$ 1.53	$ 0.29
Diluted	$ 0.55	$ 0.05	$ 1.52	$ 0.29