Cover page - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Feb. 16, 2021	Jun. 30, 2020
Document Information [Line Items]
Document Type	10-K
Document Annual Report	true
Current Fiscal Year End Date	--12-31
Document Period End Date	Dec. 31, 2020
Document Transition Report	false
Entity File Number	001-38108
Entity Registrant Name	Cumulus Media Inc
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	82-5134717
Entity Address, Address Line One	3280 Peachtree Road, NW,
Entity Address, Address Line Two	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
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	false
ICFR Auditor Attestation Flag	true
Entity Shell Company	false
Entity Public Float			$ 60.1
Entity Central Index Key	0001058623
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	FY
Amendment Flag	false
Documents Incorporated by Reference	Portions of the registration's definitive proxy statement for the 2021 Annual Meeting of Stockholders, which is expected to be filed no later than 120 days after the end of the fiscal year covered by this Annual Report on Form 10-K, have been incorporated by reference into Part III, Items 10, 11, 12, 13 and 14 of this Annual Report on Form 10-K.
Class A Common Stock
Document Information [Line Items]
Title of 12(b) Security	Class A common stock, par value $0.0000001 per share
Trading Symbol	CMLS
Security Exchange Name	NASDAQ
Entity common stock, shares outstanding (in shares)		18,041,897
Class A common stock purchase rights
Document Information [Line Items]
Title of 12(b) Security	Class A common stock purchase rights
No Trading Symbol Flag	true
Security Exchange Name	NASDAQ
Class B Common Stock
Document Information [Line Items]
Entity common stock, shares outstanding (in shares)		2,368,879