Fresh-Start Adjustment, Increase (Decrease), Property And Equipment, Gross

No definition available.

Name:	cmls_FreshStartAdjustmentIncreaseDecreasePropertyAndEquipmentGross
Namespace Prefix:	cmls_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of fresh-start adjustment to accumulated depreciation and amortization.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 852
-SubTopic 10
-Section 50
-Paragraph 7
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=6918054&loc=SL2890621-112765

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 852
-SubTopic 10
-Section 55
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=84165509&loc=d3e56426-112766

+ Details

Name:	us-gaap_FreshStartAdjustmentIncreaseDecreaseAccumulatedDepreciationAndAmortization
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Total fresh-start adjustment to property and equipment, net.

+ References

+ Details

Name:	us-gaap_FreshStartAdjustmentIncreaseDecreasePropertyAndEquipmentNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_FreshStartAdjustmentLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Useful life of long lived, physical assets used in the normal conduct of business and not intended for resale, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Examples include, but not limited to, land, buildings, machinery and equipment, office equipment, furniture and fixtures, and computer equipment.

+ References

No definition available.

+ Details

Name:	us-gaap_PropertyPlantAndEquipmentUsefulLife
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_PropertyPlantAndEquipmentByTypeAxis=us-gaap_LandMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PropertyPlantAndEquipmentByTypeAxis=cmls_BroadcastingAndOtherEquipmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PropertyPlantAndEquipmentByTypeAxis=cmls_ComputerAndSoftwareMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PropertyPlantAndEquipmentByTypeAxis=us-gaap_FurnitureAndFixturesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PropertyPlantAndEquipmentByTypeAxis=us-gaap_LeaseholdImprovementsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PropertyPlantAndEquipmentByTypeAxis=us-gaap_BuildingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PropertyPlantAndEquipmentByTypeAxis=us-gaap_ConstructionInProgressMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Fresh Start Accounting (Summary of the Components of Property, Plant, and Equipment, Net) (Detail) - USD ($) $ in Thousands		12 Months Ended
	Jun. 04, 2018	Dec. 31, 2019	Jun. 03, 2018
Fresh-Start Adjustment [Line Items]
Property and equipment, gross	$ 315,306		$ 514,051
Less: accumulated depreciation	0		(320,477)
Property and equipment, net	315,306		193,574
Land
Fresh-Start Adjustment [Line Items]
Property and equipment, gross	159,464		86,287
Broadcasting and other equipment
Fresh-Start Adjustment [Line Items]
Property and equipment, gross	58,369		248,607
Computer and capitalized software costs
Fresh-Start Adjustment [Line Items]
Property and equipment, gross	$ 11,791		34,924
Furniture and fixtures
Fresh-Start Adjustment [Line Items]
Estimated Useful Life	5 years	5 years
Property and equipment, gross	$ 4,432		15,571
Leasehold improvements
Fresh-Start Adjustment [Line Items]
Estimated Useful Life	5 years	5 years
Property and equipment, gross	$ 24,089		46,471
Buildings
Fresh-Start Adjustment [Line Items]
Property and equipment, gross	26,964		51,994
Construction in progress
Fresh-Start Adjustment [Line Items]
Property and equipment, gross	$ 30,197		$ 30,197
Minimum \| Broadcasting and other equipment
Fresh-Start Adjustment [Line Items]
Estimated Useful Life	3 years	3 years
Minimum \| Computer and capitalized software costs
Fresh-Start Adjustment [Line Items]
Estimated Useful Life	1 year	1 year
Minimum \| Buildings
Fresh-Start Adjustment [Line Items]
Estimated Useful Life	9 years	9 years
Maximum \| Broadcasting and other equipment
Fresh-Start Adjustment [Line Items]
Estimated Useful Life	30 years	30 years
Maximum \| Computer and capitalized software costs
Fresh-Start Adjustment [Line Items]
Estimated Useful Life	3 years	3 years
Maximum \| Buildings
Fresh-Start Adjustment [Line Items]
Estimated Useful Life	20 years	20 years