Stock incentive plans (Details 2) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012
Recognized stock-based compensation expense
Total stock-based compensation	$ 1,245	$ 952	$ 1,847	$ 1,945
Number of Options
Outstanding at the beginning of the period (in shares)			5,045
Granted (in shares)			887
Exercised (in shares)			(243)
Canceled/forfeited (in shares)			(532)
Outstanding at the end of the period (in shares)	5,157		5,157		5,045
Vested and expected to vest at the end of the period (in shares)	4,960		4,960
Exercisable at the end of the period (in shares)	2,726		2,726
Weighted Average Exercise Price
Outstanding at the beginning of the period (in dollars per share)			$ 6.50
Granted (in dollars per share)			$ 6.88
Exercised (in dollars per share)			$ 1.20
Canceled/forfeited (in dollars per share)			$ 11.24
Outstanding at the end of the period (in dollars per share)	$ 6.33		$ 6.33		$ 6.50
Vested and expected to vest at the end of the period (in dollars per share)	$ 6.25		$ 6.25
Exercisable at the end of the period (in dollars per share)	$ 4.01		$ 4.01
Weighted-Average Remaining Contract Life (years)
Outstanding			6 years 8 months 19 days		6 years 5 months 8 days
Vested and expected to vest at the end of the period			6 years 7 months 13 days
Exercisable at the end of the period			4 years 9 months
Aggregate Intrinsic Value
Outstanding at the beginning of the period			14,742
Outstanding at the end of the period	10,082		10,082		14,742
Vested and expected to vest at the end of the period	10,073		10,073
Exercisable at the end of the period	9,895		9,895
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)			1.07%
Dividend yield (as a percent)			0.00%
Network operations
Recognized stock-based compensation expense
Total stock-based compensation	231	105	397	111
Development and technology
Recognized stock-based compensation expense
Total stock-based compensation	142	222	99	421
Selling and marketing
Recognized stock-based compensation expense
Total stock-based compensation	340	191	458	401
General and administrative
Recognized stock-based compensation expense
Total stock-based compensation	$ 532	$ 434	$ 893	$ 1,012