Employee Benefit Plans, Assumptions and Resulting Estimates of Fair Value (Details) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Stock options
Estimates of Fair Value
Volatility		46.00%		46.00%
Risk-free interest rate		0.70%		0.80%
Expected life (years)		4 years 2 months 12 days		4 years 2 months 12 days
Dividend yield		0.00%		0.00%
Weighted-average fair value per share		$ 6.89		$ 8.46
Employee stock purchase plan
Estimates of Fair Value
Volatility	35.00%	42.00%	36.00%	47.00%
Risk-free interest rate	0.10%	0.10%	0.10%	0.10%
Expected life (years)	6 months	6 months	6 months	6 months
Dividend yield	0.00%	0.00%	0.00%	0.00%
Weighted-average fair value per share	$ 5.47	$ 4.77	$ 5.54	$ 5.53