Net loss per share attributable to common stockholders (Details 2) (USD $) In Thousands, except Share data, unless otherwise specified	0 Months Ended	6 Months Ended	0 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Apr. 01, 2013 Maximum
Stock repurchase program
Amount of common stock approved by the entity for a stock repurchase program			$ 10,000
Number of shares repurchased and retired under the stock repurchase program		155,000
Value of shares repurchased and retired under the stock repurchase program excluding commissions paid		1,056
Average price under the stock repurchase program (in dollars per share)		$ 6.81
Remaining approved amount for repurchases	$ 5,180