Goodwill and intangible assets - Other Amortizable Intangible (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017
Changes in other amortizable intangible assets
Balance at the beginning of the period	$ 38,281		$ 48,163
Additions			85
Amortization	(3,300)	$ (3,400)	(9,967)	$ (10,100)
Net balance at the end of the period	38,281		38,281
Future estimated amortization expense
Remainder of 2017					$ 3,318
2018					13,234
2019					8,483
2020					6,057
2021 and thereafter					7,189
Total	38,281		$ 48,163		38,281
Weighted Average
Future estimated amortization expense
Remaining amortization period			3 years 7 months 6 days
Affiliate relationships
Changes in other amortizable intangible assets
Balance at the beginning of the period			$ 44,468
Amortization			(9,109)
Net balance at the end of the period	35,359		35,359
Future estimated amortization expense
Total	35,359		44,468		35,359
Advertiser relationships
Changes in other amortizable intangible assets
Balance at the beginning of the period			1,792
Amortization			(414)
Net balance at the end of the period	1,378		1,378
Future estimated amortization expense
Total	1,378		1,792		1,378
Non-compete agreement
Changes in other amortizable intangible assets
Balance at the beginning of the period			1,784
Amortization			(412)
Net balance at the end of the period	1,372		1,372
Future estimated amortization expense
Total	1,372		1,784		1,372
Other intangibles
Changes in other amortizable intangible assets
Balance at the beginning of the period			119
Additions			85
Amortization			(32)
Net balance at the end of the period	172		172
Future estimated amortization expense
Total	$ 172		$ 119		$ 172