Stockholders' Equity (Details) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2010
Stock Options
Equity Incentive Plan
Maximum number of shares authorized to be issued	29.9
Shares available for issuance	11.0
Maximum contractual term	10 years
General vesting period	3 years
Expected volatility maximum period	5 years
Method and assumptions on valuation of stock options
Expected volatility (as a percent)	41.60%	45.40%
Risk-free interest rate (as a percent)	0.70%	2.10%
Expected term (in years)	5 years	5 years 1 month 6 days
Expected forfeiture rate (as a percent)	0.00%	0.00%
Expected dividend yield (as a percent)	0.00%	0.00%
Stock Options | Chief Executive Officer (CEO)
Equity Incentive Plan
Shares available for issuance	10.9
Employee Stock Purchase Plan (ESPP)
Equity Incentive Plan
Maximum number of shares authorized to be issued	3.0
Maximum contractual term	20 years
Method and assumptions on valuation of stock options
Expected volatility (as a percent)	29.00%
Risk-free interest rate (as a percent)	0.10%
Expected term (in years)	6 months
Expected forfeiture rate (as a percent)	4.60%
Expected dividend yield (as a percent)	0.00%