Intangible assets (Details 2) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Intangible assets
Historical cost	$ 30,634	$ 43,919
Accumulated Amortization	(14,579)	(24,243)
Finite-Lived Intangible Assets, Net, Total	16,055	19,676	$ 23,413
Amortization expense for fiscal years 2016 through 2020 and thereafter
2016	3,451
2017	3,221
2018	2,372
2019	1,634
2020	1,556
Thereafter	3,821
Finite-Lived Intangible Assets, Net, Total	16,055	19,676	$ 23,413
Venue contracts
Intangible assets
Historical cost	23,630	36,356
Accumulated Amortization	(11,104)	(21,582)
Finite-Lived Intangible Assets, Net, Total	12,526	14,774
Amortization expense for fiscal years 2016 through 2020 and thereafter
Finite-Lived Intangible Assets, Net, Total	12,526	14,774
Non-compete agreement
Intangible assets
Historical cost	3,590	3,840
Accumulated Amortization	(1,556)	(1,067)
Finite-Lived Intangible Assets, Net, Total	2,034	2,773
Amortization expense for fiscal years 2016 through 2020 and thereafter
Finite-Lived Intangible Assets, Net, Total	2,034	2,773
Technology
Intangible assets
Historical cost	2,310	2,300
Accumulated Amortization	(1,295)	(863)
Finite-Lived Intangible Assets, Net, Total	1,015	1,437
Amortization expense for fiscal years 2016 through 2020 and thereafter
Finite-Lived Intangible Assets, Net, Total	1,015	1,437
Advertiser relationships
Intangible assets
Historical cost	70	70
Accumulated Amortization	(48)	(34)
Finite-Lived Intangible Assets, Net, Total	22	36
Amortization expense for fiscal years 2016 through 2020 and thereafter
Finite-Lived Intangible Assets, Net, Total	22	36
Patents, trademarks and other
Intangible assets
Historical cost	1,034	1,353
Accumulated Amortization	(576)	(697)
Finite-Lived Intangible Assets, Net, Total	458	656
Amortization expense for fiscal years 2016 through 2020 and thereafter
Finite-Lived Intangible Assets, Net, Total	$ 458	$ 656