Description of business, basis of presentation and summary of significant accounting policies - Schedule of Disaggregation of Revenue (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disaggregation of Revenue [Line Items]
Total revenues	$ 2,299,497	$ 2,207,282	$ 1,903,026
Advertising & Marketing Services
Disaggregation of Revenue [Line Items]
Total revenues	1,226,607	1,106,754	1,139,642
Subscription
Disaggregation of Revenue [Line Items]
Total revenues	1,005,030	840,838	718,750
Political
Disaggregation of Revenue [Line Items]
Total revenues	38,478	233,613	23,258
Other
Disaggregation of Revenue [Line Items]
Total revenues	$ 29,382	$ 26,077	$ 21,376

Amount, excluding tax collected from customer, of revenue from satisfaction of performance obligation by transferring promised good or service to customer. Tax collected from customer is tax assessed by governmental authority that is both imposed on and concurrent with specific revenue-producing transaction, including, but not limited to, sales, use, value added and excise.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 4
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=118956577&loc=SL49130543-203045

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=118956577&loc=SL49130545-203045

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration