Commitments and Contingencies (Details) $ in Thousands		1 Months Ended	3 Months Ended		12 Months Ended
	Aug. 16, 2017	Feb. 29, 2012 USD ($)	Mar. 31, 2018 USD ($)	Sep. 30, 2017 USD ($)	Dec. 31, 2017 USD ($) case	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Mar. 01, 2018 radio_station station	Apr. 13, 2017 station	Aug. 04, 2014 shares
Loss Contingencies [Line Items]
Contractual commitments, broadcast rights					$ 860,000	$ 1,200,000
Net lease expense from continuing operations					31,000	24,000	$ 23,000
Commitments related to purchase of technology services, news and market data services, and talent contracts					$ 331,000
FCC Regulation, television and radio broadcast station license terms, years					8 years
FCC Regulation, television ownership cap, percent					39.00%
The UHF Discount, percent					50.00%
FCC Regulation, maximum reimbursement amount for required product modifications		$ 1,750,000
Federal Communications Commission Regulation, Proceeds Received From Auction					$ 191,000
Repayments of long-term debt					703,527	27,842	1,114,262
Proceeds from FCC spectrum auction					172,102	$ 0	$ 0
Proceeds from Spectrum, Sharing Arrangement, Pretax					84,000
Payments for Spectrum, Sharing Arrangements, Pretax					$ 66,000
Deferred Revenue and Other LT Liability, Useful Lives, Spectrum					30 years
Prepaid and Other LT Asset, Useful Lives, Spectrum					30 years
Number of Stations Subject to Spectrum Frequency Transition | station									22
Loss Contingency, New Claims Filed, Number | case					4
Third Party Involved in Claim, Participated in the Sale	4
Third Party Involved in Claim, Confidentiality Agreement	23
Term Loan Facility | Amended Secured Credit Facility
Loss Contingencies [Line Items]
Repayments of long-term debt				$ 102,000
tronc
Loss Contingencies [Line Items]
Investment Owned, Balance, Shares | shares										381,354
Investment Ownership Percentage										1.50%
Subsequent Event
Loss Contingencies [Line Items]
FCC Regulation, number of television stations authorized | station								39
FCC Regulation, number of radio stations authorized | radio_station								1
Subsequent Event | FCC licenses
Loss Contingencies [Line Items]
Gain (Loss) on Disposition of Intangible Assets			$ 133,000
Dreamcatcher Stations
Loss Contingencies [Line Items]
Federal Communications Commission Regulation, Proceeds Received From Auction					$ 26,000
Repayments of long-term debt				$ 12,600