Summary of significant accounting policies (Details 3) (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2013
Revenue recognition
Significant obligations related to the earned fees and collection of the related receivable	$ 0
Platform service arrangements | Minimum
Revenue recognition
Term of the arrangement used to determine revenue recognition	2 years
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