Related Party Transactions, Compensation and Other (Details) - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Nov. 30, 2015	Jul. 02, 2015	May. 31, 2006
Compensation [Abstract]
Percentage payout of revenues or net operating contribution to the portfolio managers and marketing staff who introduce, service or generate private wealth management business	40.00%
Other [Abstract]
Payable to affiliates	$ 7,687,000	$ 0
Notice period of agreement between related parties	30 days
Term of agreement between related parties	12 months
Face value of debt				$ 250,000,000
AC 4% PIK Note [Member]
Other [Abstract]
Face value of debt				$ 250,000,000
Debt instrument, interest rate	4.00%			4.00%
Loan from GGCP [Member]
Other [Abstract]
Face value of debt	$ 35,000,000
GSI [Member] | 5.5% Demand Loan [Member]
Other [Abstract]
Face value of debt		$ 16,000,000
Debt instrument, interest rate		5.50%
Interest expenses	900,000	$ 1,000,000
GAMCO [Member] | AC 4% PIK Note [Member]
Other [Abstract]
Interest expenses	800,000
GAMCO [Member] | Loan from GGCP [Member]
Other [Abstract]
Interest expenses	15,000
G.research LLC [Member] | GAMCO [Member]
Other [Abstract]
Payable to affiliates	700,000	700,000
G.research LLC [Member] | Fund Advisor [Member]
Other [Abstract]
Payable to affiliates	800,000	800,000
Significant Shareholder [Member] | Common Class A [Member]
Other [Abstract]
Shares included in the Exchange and Standstill agreement (in shares)					1,705,974
Significant Shareholder [Member] | Common Class B [Member]
Other [Abstract]
Shares included in the Exchange and Standstill agreement (in shares)						2,071,635
G G C P [Member]
Other [Abstract]
Variable costs incurred on use of aircraft	$ 432,000	458,000	$ 483,000
GBL and Teton [Member]
Other [Abstract]
Flat sub-administration agreement percentage on mutual funds	0.20%
Administration fees percentage on first tier of net assets	0.20%
First tier net assets maximum	$ 370,000,000
Administration fees percentage on second tier of net assets	0.12%
Second tier net assets maximum	$ 630,000,000
Administration fees percentage on third tier of net assets	0.10%
Third tier net assets minimum	$ 1,000,000,000
Various administrative services monthly fee	25,000	25,000	15,000
Administrative and management services	$ 2,200,000	$ 2,300,000	$ 1,800,000