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Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Jan. 01, 2019
Summary Of Significant Accounting Policies [Line Items]      
Renewable terms of FCC broadcasting licenses 8 years    
Weighted-average period before the next renewal of the Company's FCC broadcasting licenses 2 years    
Accounting Standards Update 2016-02 [Member] | Subsequent Event [Member]      
Summary Of Significant Accounting Policies [Line Items]      
Operating Lease, Liability     $ 43.1
Operating Lease, Right-of-Use Asset     38.8
New Accounting Pronouncement or Change in Accounting Principle, Cumulative Effect of Change on Retained Earnings     $ 0.9
Geographic Concentration Risk [Member] | Sales Revenue, Net [Member] | Boston, MA, Philadelphia, PA and Tampa-Saint Petersburg, FL [Member]      
Summary Of Significant Accounting Policies [Line Items]      
Radio stations contributed to net revenue 58.80% 52.50%