Net (loss) income per share attributable to common stockholders (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Numerator:
Net loss attributable to common stockholders, basic and diluted									$ (19,521)	$ (3,968)	$ 7,295
Denominator:
Weighted Average Number of Shares Outstanding, Basic									35,753,000	35,578,000	34,774,000
Effect of dilutive stock options											2,543,000
Weighted average common stock, diluted									35,753,000	35,578,000	37,317,000
Net (loss) income per share attributable to common stockholders:
Basic (in dollars per share)	$ (0.18)	$ (0.11)	$ (0.10)	$ (0.15)	$ (0.08)	$ 0.01	$ (0.01)	$ (0.03)	$ (0.55)	$ (0.11)	$ 0.21
Diluted (in dollars per share)	$ (0.18)	$ (0.11)	$ (0.10)	$ (0.15)	$ (0.08)	$ 0.01	$ (0.01)	$ (0.03)	$ (0.55)	$ (0.11)	$ 0.20
Options
Anti-dilutive securities
Anti-dilutive securities excluded from the computation of diluted net income per share											2,518,000