| Cover | Aug. 04, 2021 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Document Period End Date | Jun. 30, 2021 |
| Entity Registrant Name | CUMULUS MEDIA INC |
| Entity Central Index Key | 0001058623 |
| Amendment Flag | false |
| Entity Incorporation, State or Country Code | DE |
| Entity File Number | 001-38108 |
| Entity Tax Identification Number | 82-5134717 |
| Entity Address, Address Line One | 3280 Peachtree Road, N.W., Suite 2200 |
| Entity Address, City or Town | Atlanta |
| Entity Address, State or Province | GA |
| Entity Address, Postal Zip Code | 30305 |
| City Area Code | (404) |
| Local Phone Number | 949-0700 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Entity Emerging Growth Company | false |
| Entity Information [Line Items] | |
| Document Period End Date | Jun. 30, 2021 |
| Common Class A | |
| Cover [Abstract] | |
| Title of 12(b) Security | Class A common stock |
| Trading Symbol | CMLS |
| Security Exchange Name | NASDAQ |
| Entity Information [Line Items] | |
| Title of 12(b) Security | Class A common stock |
| Trading Symbol | CMLS |
| Security Exchange Name | NASDAQ |
