Identifiable Intangible Assets (Details) - USD ($) $ in Millions	3 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Intangible assets, net [Abstract]
Impairment on intangible assets	$ 0.0	$ 0.0
Investment Advisory Contract [Member] \| Gabelli Enterprise Mergers and Acquisitions Fund [Member]
Intangible assets, net [Abstract]
Identifiable intangible asset	1.9	1.9	$ 1.9
Investment Advisory Contract [Member] \| Bancroft Fund Ltd. and the Ellsworth Growth and Income Fund Ltd. [Member]
Intangible assets, net [Abstract]
Identifiable intangible asset	$ 1.6	$ 1.6	$ 1.6

The amount of impairment loss recognized in the period resulting from the write-down of the carrying amount of a finite-lived intangible asset to fair value.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3602-108585

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 30
-Section 50
-Paragraph 3
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=66006027&loc=d3e16373-109275

Name:	us-gaap_ImpairmentOfIntangibleAssetsFinitelived
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration