Weighted-Average Assumptions Used in Black-Scholes Option Pricing Model Which Was Used to Estimate Grant Date Fair Value per Share (Detail) (Employee Stock Option [Member], USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Employee Stock Option [Member]
Schedule of Weighted Average Assumptions for Fair Values of Stock Options[Line Items]
Shares underlying options granted (in shares)	105	1,157	1,277	2,077
Weighted-average grant date fair value (in dollars per share)	$ 37.17	$ 23.13	$ 28.49	$ 25.23
Weighted-average volatility	57.00%	64.00%	59.00%	64.00%
Weighted-average expected term (years)	4 years 4 months 24 days	4 years 2 months 12 days	4 years 4 months 24 days	4 years 7 months 6 days
Range of risk-free rates, minimum	1.00%	0.50%	0.50%	0.50%
Range of risk-free rates, maximum	1.40%	0.60%	1.40%	1.10%
Expected dividend yield	0.00%	0.00%	0.00%	0.00%