Employee Stock Plans - Stock Option Valuation Assumptions (Details) (USD $)	12 Months Ended
	Dec. 31, 2011 Years		Dec. 31, 2010 Years		Dec. 31, 2009 Years
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Volatility Rate	37.00%	[1]	37.00%	[1]	35.00%	[1]
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Term	5.5	[2]	5.2	[2]	5.9	[2]
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Risk Free Interest Rate	2.40%	[3]	2.40%	[3]	2.10%	[3]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value	$ 14.80		$ 10.39		$ 6.07

[1] Volatility is measured using historical daily price changes of the company's common stock over the expected term of the option.

[2] The expected term represents the weighted average period the option is expected to be outstanding and is based primarily on the historical exercise behavior of employees.

[3] The risk-free interest rate is based on the U.S. Treasury zero-coupon yield with a maturity that approximates the expected term of the option.