Weighted Average Assumptions Used for Fair Value of Stock Options Granted Estimated at Grant Date Using Black-Scholes Option Pricing Model (Details) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term	1 year 2 months 12 days	1 year 2 months 12 days	1 year 2 months 12 days	1 year 2 months 12 days
Expected volatility	48.00%	44.90%	49.70%	43.20%
Risk-free interest rate	0.20%	0.30%	0.20%	0.40%
Expected dividends	0.00%	0.00%	0.00%	0.00%
Weighted average fair value at grant date (in usd per share)	$ 11.99	$ 7.46	$ 11.10	$ 7.29
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term				4 years 4 months 24 days	[1]
Expected volatility				61.00%	[1]
Risk-free interest rate				1.70%	[1]
Expected dividends				0.00%	[1]
Weighted average fair value at grant date (in usd per share)				$ 10.87	[1]

[1] There were no stock options granted during the three months ended September 30, 2012 and 2011 and for the nine months ended September 30, 2012.