Net (loss) income per share attributable to common stockholders (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Numerator:
Net (loss) income attributable to common stockholders, basic and diluted	$ (399)	$ 1,461	$ (1,520)	$ 3,118
Denominator:
Weighted average common shares, basic	35,670,000	34,799,000	35,634,000	34,384,000
Dilutive effect of stock-based awards (in shares)		2,604,000		2,937,000
Weighted average common shares, dilutive	35,670,000	37,403,000	35,634,000	37,321,000
Net (loss) income per share attributable to common stockholders:
Basic (in dollars per share)	$ (0.01)	$ 0.04	$ (0.04)	$ 0.09
Diluted (in dollars per share)	$ (0.01)	$ 0.04	$ (0.04)	$ 0.08
Anti-dilutive securities
Anti-dilutive securities excluded from the computation of diluted net income per share		2,409,925		2,391,117