Stock incentive plans (Details 2) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012
Recognized stock-based compensation expense
Total stock-based compensation	$ 1,352	$ 218	$ 3,199	$ 2,163
Number of Options
Outstanding at the beginning of the period (in shares)			5,045
Granted (in shares)			951
Exercised (in shares)			(374)
Canceled/forfeited (in shares)			(802)
Outstanding at the end of the period (in shares)	4,820		4,820		5,045
Vested and expected to vest at the end of the period (in shares)	4,662		4,662
Exercisable at the end of the period (in shares)	2,729		2,729
Weighted Average Exercise Price
Outstanding at the beginning of the period (in dollars per share)			$ 6.50
Granted (in dollars per share)			$ 6.92
Exercised (in dollars per share)			$ 1.45
Canceled/forfeited (in dollars per share)			$ 10.61
Outstanding at the end of the period (in dollars per share)	$ 6.30		$ 6.30		$ 6.50
Vested and expected to vest at the end of the period (in dollars per share)	$ 6.22		$ 6.22
Exercisable at the end of the period (in dollars per share)	$ 4.18		$ 4.18
Weighted-Average Remaining Contract Life (years)
Outstanding			6 years 5 months 26 days		6 years 5 months 8 days
Vested and expected to vest at the end of the period			6 years 4 months 28 days
Exercisable at the end of the period			4 years 9 months 18 days
Aggregate Intrinsic Value
Outstanding at the beginning of the period			14,742
Outstanding at the end of the period	11,358		11,358		14,742
Vested and expected to vest at the end of the period	11,327		11,327
Exercisable at the end of the period	10,889		10,889
Significant assumptions used for newly issued stock option grants
Expected term			6 years 3 months
Expected volatility (as a percent)			49.43%
Risk free rate of return (as a percent)			1.12%
Dividend yield (as a percent)			0.00%
Network operations
Recognized stock-based compensation expense
Total stock-based compensation	241	117	638	227
Development and technology
Recognized stock-based compensation expense
Total stock-based compensation	143	(253)	242	168
Selling and marketing
Recognized stock-based compensation expense
Total stock-based compensation	301	(36)	759	366
General and administrative
Recognized stock-based compensation expense
Total stock-based compensation	$ 667	$ 390	$ 1,560	$ 1,402