Identifiable Intangible Assets (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Finite-Lived Intangible Assets [Line Items]
Impairment on intangible assets	$ 0.0	$ 0.0
Investment Advisory Contract [Member] \| Gabelli Enterprise Mergers and Acquisitions Fund [Member]
Finite-Lived Intangible Assets [Line Items]
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]
Finite-Lived Intangible Assets [Line Items]
Identifiable intangible asset	$ 1.6	$ 1.6	$ 1.6

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.

No definition available.

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- Definition

Amount after amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 30
-Section 50
-Paragraph 2
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=66006027&loc=d3e16323-109275

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- Definition

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.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-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

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