Commitments and contingencies (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2017 USD ($) item claim
Underpaid revenue share payments and related interest
Other Matters [Abstract]
Number of claim received | claim	1
Claim value	$ 4,600
Letters of Credit
Commitments and contingencies
Current issued borrowing capacity	$ 3,818
Term period of Letters of Credit agreements	1 year
Number of drafts drawn under Letters of Credit | item	0