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FCC Licenses - Discounted Cash Flow Analyses (Detail) - CBS Radio Stations Inc Entercom Boston LLC and The Entercom Divestiture Trust [Member] | 3 Months Ended | 12 Months Ended
--- | --- | ---
Sep. 30, 2020 | Mar. 31, 2020 | Dec. 31, 2020
Measurement Input, Discount Rate [Member] |  |  |
Fair Value Inputs Asset Quantitative Information [Line Items] |  |  |
Fair value assumptions inputs rate | 9.00% | 9.50% | 9.00%
Minimum [Member] |  |  |
Fair Value Inputs Asset Quantitative Information [Line Items] |  |  |
Market revenue shares at maturity | 0.60% | 0.60% | 0.60%
Operating income margins at maturity | 19.50% | 26.50% | 27.50%
Minimum [Member] | Measurement Input, Long-term Revenue Growth Rate [Member] |  |  |
Fair Value Inputs Asset Quantitative Information [Line Items] |  |  |
Fair value assumptions inputs rate | 0.50% | (14.10%) | 0.50%
Maximum [Member] |  |  |
Fair Value Inputs Asset Quantitative Information [Line Items] |  |  |
Market revenue shares at maturity | 44.40% | 39.00% | 1.10%
Operating income margins at maturity | 33.30% | 35.40% | 29.80%
Maximum [Member] | Measurement Input, Long-term Revenue Growth Rate [Member] |  |  |
Fair Value Inputs Asset Quantitative Information [Line Items] |  |  |
Fair value assumptions inputs rate | 18.80% | 7.90% | 1.40%

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