Net loss per share attributable to common stockholders (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Apr. 01, 2013
Numerator:
Net loss attributable to common stockholders, basic and diluted	$ (8,017)	$ (7,266)	$ (14,897)	$ (17,250)
Denominator:
Weighted average common stock, basic and diluted (in shares)	39,286	37,944	38,997	37,749
Net loss per share attributable to common stockholders:
Basic and diluted (in dollars per share)	$ (0.20)	$ (0.19)	$ (0.38)	$ (0.46)
Stock repurchase program
Remaining approved amount for repurchases	$ 5,180		$ 5,180
Maximum
Stock repurchase program
Amount of common stock approved by the entity for a stock repurchase program					$ 10,000