Goodwill and Identifiable Intangible Assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Goodwill and Identifiable Intangible Assets [Abstract]
Goodwill	$ 200	$ 200
Intangible assets, net [Abstract]
Impairment on intangible assets	589	0
Gabelli Enterprise Mergers and Acquisitions Fund [Member]
Intangible assets, net [Abstract]
Impairment on intangible assets	589	0
Bancroft Fund [Member]
Intangible assets, net [Abstract]
Impairment on intangible assets	0
Ellsworth Fund [Member]
Intangible assets, net [Abstract]
Impairment on intangible assets	0
Investment Advisory Contract [Member] | Gabelli Enterprise Mergers and Acquisitions Fund [Member]
Intangible assets, net [Abstract]
Identifiable intangible asset	1,300	1,900
Investment Advisory Contract [Member] | Bancroft Fund Ltd. and the Ellsworth Growth and Income Fund Ltd. [Member]
Intangible assets, net [Abstract]
Identifiable intangible asset	$ 1,600	$ 1,600