Goodwill and intangible assets (Details 3) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Intangible assets
Historical cost	$ 43,919	$ 43,974
Accumulated Amortization	(24,243)	(20,561)
Net Book Value	19,676	23,413	10,594
Amortization expense for fiscal years 2015 through 2019 and thereafter
2015	3,525
2016	3,451
2017	3,218
2018	2,370
2019	1,625
Thereafter	5,487
Net Book Value	19,676	23,413	10,594
Venue contracts
Intangible assets
Weighted Average Life	10 years	10 years
Historical cost	36,356	36,356
Accumulated Amortization	(21,582)	(19,314)
Net Book Value	14,774	17,042
Amortization expense for fiscal years 2015 through 2019 and thereafter
Net Book Value	14,774	17,042
Non-compete agreement
Intangible assets
Weighted Average Life	5 years	5 years
Historical cost	3,840	3,840
Accumulated Amortization	(1,067)	(224)
Net Book Value	2,773	3,616
Amortization expense for fiscal years 2015 through 2019 and thereafter
Net Book Value	2,773	3,616
Technology
Intangible assets
Weighted Average Life	6 years	6 years
Historical cost	2,300	2,300
Accumulated Amortization	(863)	(441)
Net Book Value	1,437	1,859
Amortization expense for fiscal years 2015 through 2019 and thereafter
Net Book Value	1,437	1,859
Advertiser relationships
Intangible assets
Weighted Average Life	5 years	5 years
Historical cost	70	70
Accumulated Amortization	(34)	(20)
Net Book Value	36	50
Amortization expense for fiscal years 2015 through 2019 and thereafter
Net Book Value	36	50
Patents, trademarks and other
Intangible assets
Weighted Average Life	6 years	6 years
Historical cost	1,353	1,408
Accumulated Amortization	(697)	(562)
Net Book Value	656	846
Amortization expense for fiscal years 2015 through 2019 and thereafter
Net Book Value	$ 656	$ 846