Carrying value as of the balance sheet date of obligations incurred and payable, pertaining to costs that are statutory in nature, are incurred on contractual obligations, or accumulate over time and for which invoices have not yet been received or will not be rendered. This element may include payable to brokers, income taxes payable and deferred tax liabilities, capital lease obligation, compensation payable, mandatorily redeemable noncontrolling interests, and accrued expenses and other liabilities.

No definition available.

Investments in Partnerships, Offshore Funds and Variable Interest Entities, Part II (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Assets [Abstract]
Cash and cash equivalents at end of period	$ 298,224				$ 210,451				$ 298,224	$ 210,451	$ 190,608	$ 276,340
Investments in securities	259,537us-gaap_MarketableSecurities				231,228us-gaap_MarketableSecurities				259,537us-gaap_MarketableSecurities	231,228us-gaap_MarketableSecurities
Investments in sponsored investment companies	39,537				44,042				39,537	44,042
Investments in partnerships	107,637gbl_InvestmentsInPartnerships				95,992gbl_InvestmentsInPartnerships				107,637gbl_InvestmentsInPartnerships	95,992gbl_InvestmentsInPartnerships
Receivable from brokers	76,079				49,461				76,079	49,461
Total assets	866,430us-gaap_Assets				709,485us-gaap_Assets				866,430us-gaap_Assets	709,485us-gaap_Assets
Liabilities and Equity [Abstract]
Securities sold, not yet purchased	10,595				6,178				10,595	6,178
Redeemable noncontrolling interests	68,334				6,751				68,334	6,751
Total equity	527,795				460,182				527,795	460,182	370,934	407,411
Total liabilities and equity	866,430				709,485				866,430	709,485
Condensed Consolidated Statements of Income [Abstract]
Total revenues									440,382us-gaap_Revenues	397,562us-gaap_Revenues	344,281us-gaap_Revenues
Total expenses									280,856us-gaap_CostsAndExpenses	255,150us-gaap_CostsAndExpenses	233,151us-gaap_CostsAndExpenses
Operating income	41,904us-gaap_OperatingIncomeLoss	43,586us-gaap_OperatingIncomeLoss	37,537us-gaap_OperatingIncomeLoss	36,499us-gaap_OperatingIncomeLoss	47,173us-gaap_OperatingIncomeLoss	32,728us-gaap_OperatingIncomeLoss	31,784us-gaap_OperatingIncomeLoss	30,727us-gaap_OperatingIncomeLoss	159,526us-gaap_OperatingIncomeLoss	142,412us-gaap_OperatingIncomeLoss	111,130us-gaap_OperatingIncomeLoss
Total other income, net									8,095us-gaap_NonoperatingIncomeExpense	41,139us-gaap_NonoperatingIncomeExpense	6,186us-gaap_NonoperatingIncomeExpense
Income before income taxes									167,621	183,551	117,316
Income tax provision									62,505us-gaap_IncomeTaxExpenseBenefit	66,186us-gaap_IncomeTaxExpenseBenefit	41,721us-gaap_IncomeTaxExpenseBenefit
Net income									105,116us-gaap_ProfitLoss	117,365us-gaap_ProfitLoss	75,595us-gaap_ProfitLoss
Net income/(loss) attributable to noncontrolling interests									(4,274)	512	56
Net income attributable to GAMCO Investors, Inc.'s shareholders									109,390us-gaap_NetIncomeLoss	116,853us-gaap_NetIncomeLoss	75,539us-gaap_NetIncomeLoss
VIE [Member]
Assets [Abstract]
Investments in partnerships	13,434				15,540				13,434	15,540
Liabilities and Equity [Abstract]
Accrued expense and other liabilities	(12)				(2,022)				(12)	(2,022)
Redeemable noncontrolling interests	(794)				(1,120)				(794)	(1,120)
GAMCO's net interests in consolidated VIEs	12,628				12,398				12,628	12,398
As Reported [Member]
Assets [Abstract]
Cash and cash equivalents at end of period	298,224				210,451				298,224	210,451
Investments in securities	299,074				275,270				299,074	275,270
Investments in partnerships	107,637				95,992				107,637	95,992
Receivable from brokers	76,079				49,461				76,079	49,461
Investment advisory fees receivable	41,872				51,506				41,872	51,506
Other asset	43,544				26,805				43,544	26,805
Total assets	866,430				709,485				866,430	709,485
Liabilities and Equity [Abstract]
Securities sold, not yet purchased	10,595				6,178				10,595	6,178
Accrued expense and other liabilities	147,543				124,463				147,543	124,463
Total Debt	112,163				111,911				112,163	111,911
Redeemable noncontrolling interests	68,334				6,751				68,334	6,751
Total equity	527,795				460,182				527,795	460,182
Total liabilities and equity	866,430				709,485				866,430	709,485
Prior to Consolidations [Member]
Assets [Abstract]
Cash and cash equivalents at end of period	298,149				209,667				298,149	209,667
Investments in securities	239,980				276,244				239,980	276,244
Investments in partnerships	111,380				98,494				111,380	98,494
Receivable from brokers	24,301				35,151				24,301	35,151
Investment advisory fees receivable	42,102				52,509				42,102	52,509
Other asset	43,393				27,433				43,393	27,433
Total assets	759,305				699,498				759,305	699,498
Liabilities and Equity [Abstract]
Securities sold, not yet purchased	9,991				6,049				9,991	6,049
Accrued expense and other liabilities	109,356				121,356				109,356	121,356
Total Debt	112,163				111,911				112,163	111,911
Redeemable noncontrolling interests	0				0				0	0
Total equity	527,795				460,182				527,795	460,182
Total liabilities and equity	759,305				699,498				759,305	699,498
Condensed Consolidated Statements of Income [Abstract]
Total revenues									441,380	399,565	346,195
Total expenses									279,823	254,153	232,313
Operating income									161,557	145,412	113,882
Total other income, net									10,221	37,676	3,264
Income before income taxes									171,778	183,088	117,146
Income tax provision									62,505	66,186	41,721
Net income									109,273	116,902	75,425
Net income/(loss) attributable to noncontrolling interests									(117)	49	(114)
Net income attributable to GAMCO Investors, Inc.'s shareholders									109,390	116,853	75,539
CFFs [Member]
Assets [Abstract]
Cash and cash equivalents at end of period	(11)				450				(11)	450
Investments in securities	0				0				0	0
Investments in partnerships	4,438				6,517				4,438	6,517
Receivable from brokers	0				0				0	0
Investment advisory fees receivable	(6)				(24)				(6)	(24)
Other asset	0				(2,339)				0	(2,339)
Total assets	4,421				4,604				4,421	4,604
Liabilities and Equity [Abstract]
Securities sold, not yet purchased	0				0				0	0
Accrued expense and other liabilities	22				165				22	165
Total Debt	0				0				0	0
Redeemable noncontrolling interests	4,399				4,439				4,399	4,439
Total equity	0				0				0	0
Total liabilities and equity	4,421				4,604				4,421	4,604
Condensed Consolidated Statements of Income [Abstract]
Total revenues									(28)	(53)	2
Total expenses									62	175	132
Operating income									(90)	(228)	(130)
Total other income, net									13	475	216
Income before income taxes									(77)	247	86
Income tax provision									0	0	0
Net income									(77)	247	86
Net income/(loss) attributable to noncontrolling interests									(77)	247	86
Net income attributable to GAMCO Investors, Inc.'s shareholders									0	0	0
Partnerships [Member]
Assets [Abstract]
Cash and cash equivalents at end of period	86				334				86	334
Investments in securities	7,801				7,473				7,801	7,473
Investments in partnerships	(8,181)				(9,019)				(8,181)	(9,019)
Receivable from brokers	623				0				623	0
Investment advisory fees receivable	(2)				(14)				(2)	(14)
Other asset	0				1,592				0	1,592
Total assets	327				366				327	366
Liabilities and Equity [Abstract]
Securities sold, not yet purchased	0				0				0	0
Accrued expense and other liabilities	24				29				24	29
Total Debt	0				0				0	0
Redeemable noncontrolling interests	303				337				303	337
Total equity	0				0				0	0
Total liabilities and equity	327				366				327	366
Condensed Consolidated Statements of Income [Abstract]
Total revenues									(3)	(15)	(6)
Total expenses									44	47	39
Operating income									(47)	(62)	(45)
Total other income, net									50	111	67
Income before income taxes									3	49	22
Income tax provision									0	0	0
Net income									3	49	22
Net income/(loss) attributable to noncontrolling interests									3	49	22
Net income attributable to GAMCO Investors, Inc.'s shareholders									0	0	0
Offshore Funds [Member]
Assets [Abstract]
Cash and cash equivalents at end of period	0				0				0	0
Investments in securities	51,293				(8,447)				51,293	(8,447)
Investments in partnerships	0				0				0	0
Receivable from brokers	51,155				14,310				51,155	14,310
Investment advisory fees receivable	(222)				(965)				(222)	(965)
Other asset	151				119				151	119
Total assets	102,377				5,017				102,377	5,017
Liabilities and Equity [Abstract]
Securities sold, not yet purchased	604				129				604	129
Accrued expense and other liabilities	38,141				2,913				38,141	2,913
Total Debt	0				0				0	0
Redeemable noncontrolling interests	63,632				1,975				63,632	1,975
Total equity	0				0				0	0
Total liabilities and equity	102,377				5,017				102,377	5,017
Condensed Consolidated Statements of Income [Abstract]
Total revenues									(967)	(1,935)	(1,910)
Total expenses									927	775	667
Operating income									(1,894)	(2,710)	(2,577)
Total other income, net									(2,189)	2,877	2,639
Income before income taxes									(4,083)	167	62
Income tax provision									0	0	0
Net income									(4,083)	167	62
Net income/(loss) attributable to noncontrolling interests									(4,083)	167	62
Net income attributable to GAMCO Investors, Inc.'s shareholders									$ 0	$ 0	$ 0