Summary of significant accounting policies (Details 4) (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2013 item	Dec. 31, 2012	Dec. 31, 2011
Advertising, marketing and promotion costs
Capitalized advertising production costs	$ 0	$ 0	$ 0
Advertising expenses	2,302	2,374	1,393
Assumptions that were used to calculate the grant date fair value of employee stock option grants
Expected term	6 years 3 months	5 years 10 months 24 days	6 years 4 months 24 days
Expected volatility (as a percent)	49.31%	48.90%	49.80%
Risk-free interest rate (as a percent)	1.34%	0.90%	2.40%
Dividend yield (as a percent)	0.00%	0.00%	0.00%
Stock-based compensation expense recognized for non-employee	$ 30	$ 372	$ 515
Dividends declared on common stock (in dollars per share)	$ 0.00
Dividends paid on common stock (in dollars per share)	$ 0.00
Number of dividend payouts anticipated in the foreseeable future	0
Platform service arrangements | Minimum
Revenue recognition
Term of the arrangement used to determine revenue recognition	1 year
Platform service arrangements | Maximum
Revenue recognition
Term of the arrangement used to determine revenue recognition	5 years
Telecom operations and wholesale partner arrangements | Minimum
Revenue recognition
Term of the arrangement used to determine revenue recognition	3 years
Telecom operations and wholesale partner arrangements | Maximum
Revenue recognition
Term of the arrangement used to determine revenue recognition	15 years