Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016
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	3 years
Advertising agency commissions of gross revenue	15.00%
Barter sales revenue from Broadcasting Service	$ 9.6	$ 5.3
Barter sales expenses from Broadcasting Service	$ 9.6	$ 5.1
Geographic Concentration Risk [Member] \| Sales Revenue, Net [Member] \| Boston, MA and Philadelphia, PA [Member]
Summary Of Significant Accounting Policies [Line Items]
Radio stations contributed to net revenue	41.10%
Geographic Concentration Risk [Member] \| Sales Revenue, Net [Member] \| Charlotte, NC and Tampa-Saint Petersburg, FL [Member]
Summary Of Significant Accounting Policies [Line Items]
Radio stations contributed to net revenue	22.10%	43.50%
LN2 DB, LLC [Member]
Summary Of Significant Accounting Policies [Line Items]
Carrying value of the investment	$ 1.0	$ 1.0
Quu Inc. [Member]
Summary Of Significant Accounting Policies [Line Items]
Carrying value of the investment	$ 0.9	$ 0.9

General advertising agency commission rate on gross revenue.

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The renewable term generally granted by the FCC for radio broadcasting licenses.

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Summary Of Significant Accounting Policies [Line Items]

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Weighted-average period before the next renewal of the company's FCC broadcasting licenses.

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- Definition

Total expense recognized from advertising barter transactions for each income statement presented.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 605
-SubTopic 20
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Total revenue recognized from advertising barter transactions for each income statement presented.

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For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

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Cost of the investment.

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