Weighted Average Assumptions and Fair Values Used for Employee Stock Options and Restricted Stock Units (Detail) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Share based Compensation Arrangement by Share based Payment Award, Fair Value Assumptions, Method Used [Line Items]
Weighted average grant date fair value-restricted stock units	$ 63.07
Equity Incentive Plan
Share based Compensation Arrangement by Share based Payment Award, Fair Value Assumptions, Method Used [Line Items]
Weighted average expected term of options in years	4 years 7 months 6 days	4 years 7 months 6 days	4 years 6 months
Weighted average expected volatility of the Company's underlying common stock	50.40%	48.70%	45.10%
Risk-free interest rate	0.83%	2.00%	2.23%
Expected dividend yield	$ 0.00	$ 0.00	$ 0.00
Weighted average grant date fair value-stock options	$ 27.00	$ 25.12	$ 19.15
Weighted average grant date fair value-restricted stock units	$ 63.07	$ 59.69	$ 46.96