Document and Entity Information - shares	6 Months Ended
	Jun. 30, 2018	Aug. 13, 2018
Document Information [Line Items]
Entity Registrant Name	CUMULUS MEDIA INC
Trading Symbol	CMLS
Entity Central Index Key	0001058623
Current Fiscal Year End Date	--12-31
Entity Filer Category	Smaller Reporting Company
Document Type	10-Q
Document Period End Date	Jun. 30, 2018
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	Q2
Amendment Flag	false
Class A common stock
Document Information [Line Items]
Entity Common Stock, Shares Outstanding		12,613,356
Class B common stock
Document Information [Line Items]
Entity Common Stock, Shares Outstanding		3,743,447