Commitments and contingencies (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Commitments and contingencies
Rent expense for leases	$ 25,099	$ 29,434	$ 20,234
Interest expense associated with the capital leases	58	33	15
Rent expense for leases of office facilities	2,995	1,621	1,227
Sublease income included in rent expenses	$ 13	27	$ 54
Term of capital lease	3 years
Capital Leases
2016	$ 1,610
2017	1,686
2018	554
2019	0
2020	0
Thereafter	0
Minimum lease payments	3,850
Less: Amounts representing interest ranging from 2.4% to 7.7%	(23)
Capital leases minimum lease payments	3,827
Current portion	1,610	309
Non-current portion	2,217	$ 381
Operating Leases and Venue Guarantees
2016	11,536
2017	10,431
2018	9,567
2019	7,273
2020	6,961
Thereafter	29,777
Minimum lease payments	$ 75,545
Minimum
Capital and operating leases
Interest rate (as a percent)	2.40%
Maximum
Capital and operating leases
Initial term of operating leases	20 years
Interest rate (as a percent)	7.70%