GAIN Capital 10-Q 12 Nov 13 2013 Q3 Quarterly report Financial data

Document_and_Entity_Informatio

Document and Entity Information	9 Months Ended
	Sep. 30, 2013	Nov. 11, 2013
Document Documentand Entity Information [Abstract]	'	'
Entity Registrant Name	'GAIN CAPITAL HOLDINGS, INC.	'
Trading Symbol	'GCAP	'
Entity Central Index Key	'0001444363	'
Current Fiscal Year End Date	'--12-31	'
Entity Filer Category	'Accelerated Filer	'
Document Type	'10-Q	'
Document Period End Date	30-Sep-13	'
Document Fiscal Year Focus	'2013	'
Document Fiscal Period Focus	'Q3	'
Amendment Flag	'false	'
Entity Common Stock, Shares Outstanding	'	39,610,053

Condensed_Consolidated_Balance

Condensed Consolidated Balance Sheet (USD $)	Sep. 30, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified
ASSETS:	'	'
Cash and cash equivalents	$28,323	$36,820
Cash and securities held for customers	684,071	446,311
Short term investments, at fair value	804	1,437
Receivables from banks and brokers, ($10,606) and $810, respectively, at fair value	186,438	89,916
Property and equipment, net of accumulated depreciation	18,631	11,023
Prepaid assets	11,188	7,704
Goodwill	11,406	9,030
Intangible assets, net	36,313	9,868
Other assets, net	34,970	17,153
Total assets	1,012,144	629,262
Liabilities	'	'
Payables to customers, brokers, dealers, FCMs and other regulated entities	684,071	446,311
Accrued compensation and benefits	11,188	6,055
Accrued expenses and other liabilities	56,032	12,585
Income tax payable	4,801	1,481
Loan payable	33,200	0
Total liabilities	789,292	466,432
GAIN Capital Holdings, Inc. Shareholders' equity	'	'
Common stock ($0.00001 par value; 60 million shares authorized; 41,331,924 shares issued and 39,548,179 shares outstanding as of September 30, 2013; 36,486,036 shares issued and 34,924,095 shares outstanding as of December 31, 2012)	0	0
Accumulated other comprehensive (loss)/income	1,366	1,249
Additional paid-in capital	124,439	85,089
Treasury stock, at cost (1,783,745 shares at September 30, 2013 and 1,561,941 at December 31, 2012, respectively)	-9,267	-8,280
Retained earnings	106,314	84,772
Total GAIN Capital Holdings, Inc. Shareholders' equity	222,852	162,830
Total liabilities and shareholders' equity	$1,012,144	$629,262

Condensed_Consolidated_Balance1

Condensed Consolidated Balance Sheet (Parenthetical) (USD $)	Sep. 30, 2013	Dec. 31, 2012
In Thousands, except Share data, unless otherwise specified
Statement of Financial Position [Abstract]	'	'
Receivables from banks and brokers, Fair Value	($10,606)	$810
Common Stock, par value	$0.00	$0.00
Common Stock, shares authorized	60,000,000	60,000,000
Common Stock, shares issued	41,331,924	36,486,036
Common Stock, shares outstanding	39,548,179	34,924,095
Treasury stock, shares	1,783,745	1,561,941

Condensed_Consolidated_Stateme

Condensed Consolidated Statements of Operations and Comprehensive Income (USD $)	3 Months Ended		9 Months Ended
In Thousands, except Share data, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
REVENUE:	'	'	'	'
Trading revenue	$50,919	$34,316	$143,708	$104,590
Commission revenue	12,662	5,435	37,749	13,523
Other revenue	-3,010	157	1,700	825
Total non-interest revenue	60,571	39,908	183,157	118,938
Interest revenue	207	119	629	405
Interest expense	-180	-42	-428	-428
Total net interest revenue (expense)	27	77	201	-23
Net revenue	60,598	39,985	183,358	118,915
EXPENSES:	'	'	'	'
Employee compensation and benefits	16,222	11,905	45,028	35,424
Selling and marketing	5,713	5,748	15,858	20,116
Trading expenses and commissions	18,026	8,927	51,075	26,862
General and administrative	5,710	5,261	16,669	14,694
Depreciation and amortization	1,852	1,126	5,234	3,234
Purchased intangible amortization	486	565	1,687	3,450
Communications and technology	2,249	1,891	6,503	5,607
Bad debt provision	807	46	1,193	248
Business Combination, Acquisition Related Costs	451	85	1,456	85
Restructuring	439	0	439	634
Total	51,955	35,554	145,142	110,354
INCOME BEFORE INCOME TAX EXPENSE	8,643	4,431	38,216	8,561
Income tax expense	3,043	1,210	11,172	2,152
NET INCOME APPLICABLE TO GAIN CAPITAL HOLDINGS, INC.	5,600	3,221	27,044	6,409
Other comprehensive income /(loss), net of tax:	'	'	'	'
Foreign currency translation adjustment	3,983	210	117	638
NET COMPREHENSIVE INCOME APPLICABLE TO GAIN CAPITAL HOLDINGS, INC.	$9,583	$3,431	$27,161	$7,047
Earnings per common share:	'	'	'	'
Basic (usd per share)	$0.16	$0.09	$0.76	$0.18
Diluted (usd per share)	$0.14	$0.08	$0.69	$0.16
Weighted average common shares outstanding used in computing earnings per common share:	'	'	'	'
Basic (shares)	36,062,659	35,250,404	35,563,701	34,893,622
Diluted (shares)	39,730,857	38,560,657	38,722,667	38,927,673

Condensed_Consolidated_Stateme1

Condensed Consolidated Statement of Changes in Shareholders' Equity (USD $)	Total	Common Stock	Treasury Stock	Additional Paid in Capital	Accumulated Retained Earnings	Accumulated Other Comprehensive Income/(loss)	Equity Issued in Business Combination [Member]	GFT Equity issuance [Member]
In Thousands, except Share data, unless otherwise specified	USD ($)		USD ($)	USD ($)	USD ($)	USD ($)		USD ($)
BEGINNING BALANCE at Dec. 31, 2012	$162,830	'	($8,280)	$85,089	$84,772	$1,249	'	'
BEGINNING BALANCE (in shares) at Dec. 31, 2012	'	34,924,095	'	'	'	'	'	'
Increase (Decrease) in Stockholders' Equity [Roll Forward]	'	'	'	'	'	'	'	'
Exercise of options (in shares)	'	864,834	'	'	'	'	'	'
Exercise of options	1,524	'	'	1,524	'	'	'	'
Common Stock, Shares, Issued	41,331,924	'	'	'	'	'	3,625,721	'
Additional Paid in Capital	35,079	'	'	'	'	'	'	'
Conversion of restricted stock into common stock (in shares)	'	303,074	'	'	'	'	'	'
Conversion of restricted stock into common stock	0	'	'	0	'	'	'	'
Shares issued under employee stock purchase plan (in shares)	'	52,259	'	'	'	'	'	'
Shares issued under employee stock purchase plan	181	'	'	181	'	'	'	'
Repurchase of shares, (in shares)	'	-221,804	'	'	'	'	'	'
Repurchase of shares, value	-987	'	-987	'	'	'	'	'
Stock compensation expense	2,272	'	'	2,272	'	'	'	'
Foreign currency translation adjustment	117	'	'	'	'	117	'	'
Tax benefit of stock options exercises	373	'	'	373	'	0	'	'
Other	-233	'	'	-79	-154	'	'	'
Dividend payment (usd per share)	-5,348	'	'	'	-5,348	'	'	'
Net income	27,044	'	'	'	27,044	'	'	'
ENDING BALANCE at Sep. 30, 2013	222,852	'	-9,267	124,439	106,314	1,366	'	222,852
ENDING BALANCE (in shares) at Sep. 30, 2013	'	39,548,179	'	'	'	'	'	'
BEGINNING BALANCE at Jun. 30, 2013	'	'	'	'	'	'	'	'
Increase (Decrease) in Stockholders' Equity [Roll Forward]	'	'	'	'	'	'	'	'
Common Stock, Shares, Issued	41,331,924	'	'	'	'	'	3,625,721	'
Additional Paid in Capital	35,079	'	'	'	'	'	'	'
Net income	5,600	'	'	'	'	'	'	'
ENDING BALANCE at Sep. 30, 2013	$222,852	'	'	'	'	'	'	$222,852

Condensed_Consolidated_Stateme2

Condensed Consolidated Statement of Changes in Shareholders' Equity (Parenthetical) (USD $)	9 Months Ended
	Sep. 30, 2013
Statement of Stockholders' Equity [Abstract]	'
Dividend payment, per share	$0.05

Condensed_Consolidated_Stateme3

Condensed Consolidated Statements of Cash Flows (USD $)	9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012
CASH FLOWS FROM OPERATING ACTIVITIES:	'	'
Net income	$27,044	$6,409
Adjustments to reconcile net income to cash provided by operating activities	'	'
(Loss)/gain on foreign currency exchange rates	2,243	1,908
Depreciation and amortization	6,921	6,684
Deferred taxes	2,076	-1,080
Amortization of deferred financing costs	0	51
Bad debt provision	1,193	216
Loss on disposal of fixed assets	0	34
Stock compensation expense	2,272	2,623
Changes in operating assets and liabilities:	'	'
Cash and securities held for customers	-13,173	-10,760
Receivables from banks and brokers	-37,952	1,000
Prepaid assets	-1,617	1,637
Other assets	-5,494	-150
Payables to customers, brokers, dealers, FCMs and other regulated entities	13,173	10,512
Accrued compensation and benefits	5,130	-97
Accrued expenses and other liabilities	5,364	61
Income tax payable	3,190	46
Cash provided by operating activities	10,370	19,094
CASH FLOWS FROM INVESTING ACTIVITIES:	'	'
Purchases of property and equipment	-4,351	-6,486
Payments to Acquire Held-to-maturity Securities	0	-44,954
Sale of Treasury Bills	606	0
Business Acquisition, Purchase Price Allocation, Assets Acquired (Liabilities Assumed), Net	-4,219	-6,813
Cash used for investing activities	-7,964	-58,253
CASH FLOWS FROM FINANCING ACTIVITIES:	'	'
Contractual payments for acquired assets	-2,420	-1,818
Principal payment on notes payable	0	-7,875
Proceeds from exercise of stock options	1,524	1,873
Proceeds from employee stock purchase plan	181	216
Purchase of treasury stock	-987	-1,439
Tax benefit from employee stock option exercises	373	-24
Dividend payment	-5,348	-5,212
Cash used for financing activities	-6,677	-14,279
Effect of exchange rate changes on cash and cash equivalents	-4,226	868
DECREASE IN CASH AND CASH EQUIVALENTS	-8,497	-52,570
CASH AND CASH EQUIVALENTS-Beginning of period	36,820	60,221
CASH AND CASH EQUIVALENTS-End of period	28,323	7,651
Cash (paid) / received during the year for:	'	'
Interest	-190	-189
Taxes	-5,540	3,279
Noncash or Part Noncash Acquisition, Value of Assets Acquired	'	835
Non-cash investing activities:	'	'
Purchase of fixed assets in accrued expense and other liabilities	$0	($2,593)

DESCRIPTION_OF_BUSINESS_AND_BA

DESCRIPTION OF BUSINESS AND BASIS OF PRESENTATION	9 Months Ended
	Sep. 30, 2013
Accounting Policies [Abstract]	'
DESCRIPTION OF BUSINESS AND BASIS OF PRESENTATION	'
	DESCRIPTION OF BUSINESS AND BASIS OF PRESENTATION
	Description of Business
	GAIN Capital Holdings, Inc., together with its subsidiaries (the “Company”) is a Delaware corporation formed and incorporated on March 24, 2006. GAIN Holdings, LLC is a wholly-owned subsidiary of GAIN Capital Holdings, Inc., and owns all outstanding membership units in GAIN Capital Group, LLC (“Group, LLC”), the primary regulated entity in the United States of America.
	Group, LLC is a retail foreign exchange dealer (“RFED”) and a registered Futures Commission Merchant (“FCM”) with the Commodity Futures Trading Commission (“CFTC”). As such, it is subject to the regulations of the CFTC, an agency of the U.S. Government, and the rules of the National Futures Association (“NFA”), an industry self-regulatory organization.
	The following list includes each of the Company’s significant U.S. and international regulated subsidiaries:
	GAIN Capital Group, LLC
	GAIN Capital-Forex.com U.K., Ltd.
	Forex.com Japan Co., Ltd.
	GAIN Capital Forex.com Australia Pty. Ltd.
	GAIN Capital-Forex.com Hong Kong Ltd.
	GAIN Capital-Forex.com Canada, Ltd.
	GAIN GTX, LLC
	Global Futures & Forex, Ltd.
	GFT Global Markets UK Ltd.
	GFT Global Markets Asia Pte., Ltd.
	In September 2013, the Company purchased all of the outstanding share capital of Global Futures & Forex, Ltd., a Michigan corporation ("GFT"). See Note 5 "Acquisitions" for further details related to this acquisition.
	During 2012, the Company purchased all of the outstanding shares of capital stock of Paragon Futures Group, Inc., a Delaware corporation. Paragon owned all of the membership interests of Open E Cry, LLC (together “OEC”), an internet based futures business subject to the regulations of the CFTC. In November 2012, OEC was merged into Group, LLC. See Note 5 "Acquisitions" for further details related to this acquisition.
	Basis of Presentation and Principles of Consolidation
	The accompanying unaudited condensed consolidated financial statements reflect all adjustments, all of which are normal recurring adjustments that, in the opinion of management, are necessary for a fair presentation of the financial statements for the interim periods. The unaudited condensed consolidated financial statements have been prepared in accordance with the regulations of the Securities and Exchange Commission ("SEC") for interim financial statements, and, in accordance with SEC rules, omit or condense certain information and footnote disclosures. Results for the interim periods are not necessarily indicative of results to be expected for any other interim period or for the full year. These financial statements should be read in conjunction with the consolidated financial statements and related notes included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2012 filed with the SEC on March 18, 2013 (the “2012 Form 10-K”). There have been no changes in the significant accounting policies from those included in the 2012 Form 10-K. The condensed consolidated financial statements include the accounts of the Company and its wholly-owned subsidiaries, after the elimination of inter-company transactions and balances.
	In connection with the preparation of this Quarterly Report on Form 10-Q, the Company identified an error in the income tax provision recorded in the year ended December 31, 2010, and in the corresponding recognized tax assets and liabilities. The Company considered guidance in ASC 250, including ASC 250-10-S99 SEC, formerly Staff Accounting Bulletin Release Topic 1.M, Materiality (“SAB 99”), and SEC Staff Accounting Bulletin Release Topic 1.N, Considering the Effect of Prior Year Misstatements when Quantifying Misstatements in Current Year Financial Statements (“SAB 108”), and concluded that the error did not constitute a material change to its previously issued consolidated financial statements. However, in order to accurately reflect the tax charge in the appropriate period, the Company has restated the Other assets, net, Income tax payable and Retained earnings balances as of December 31, 2012 to reflect the adjustment as if it had been made in the correct period. The correction of this error had no impact on amounts presented on the Consolidated Statements of Operations and Comprehensive Income or Consolidated Statements of Cash Flows presented herein.
	The table below describes the impact on the Consolidated Balance Sheet of the changes described above:
		As of December 31,
		Restated 2012	As reported 2012
	Other assets, net	17,153	17,804
	Income tax payable	1,481	1,275
	Retained earnings	84,772	85,629
	In the three and nine months ended September 30, 2012, the Company presented certain revenue related to its securities business in “Other revenue” on the Condensed Consolidated Statements of Operations and Comprehensive Income. However, due to the expansion of the Company’s institutional business in recent periods, and the addition of the exchange based business, OEC, the Company has reclassified revenue from these businesses from “Institutional trading revenue” and “Other Revenue” respectively to “Commission Revenue” in the Condensed Consolidated Statements of Operations and Comprehensive Income presented herein. The change in presentation had no effect on the total non-interest revenue or total net revenue.
	Previously, the Company presented separately certain administrative expense related items. In an effort to align the presentation of expenses with competitors in the industry in order to enable easier comparisons, the Company has consolidated certain captions. The Company has presented amounts previously presented in “Bank fees”, “Occupancy and equipment”, “Professional fees” and “Other” under the new caption of “General and administrative”. Additionally, the Company has presented amounts previously presented in “Communications and data processing” and “Product development, software and maintenance” under the new caption “Communications and technology”. The change in presentation had no effect on the total expenses.
	Previously, the Company presented certain acquisition expenses in "General and administrative". To provide greater transparency over these costs and enable easier comparison of operating performance, the Company has reclassified these costs to "Acquisition expense". The change in presentation has no effect on the total expenses.

RECENT_ACCOUNTING_PRONOUNCEMEN

RECENT ACCOUNTING PRONOUNCEMENTS	9 Months Ended
	Sep. 30, 2013
Accounting Changes and Error Corrections [Abstract]	'
RECENT ACCOUNTING PRONOUNCEMENTS	'
	RECENT ACCOUNTING PRONOUNCEMENTS
	In July 2013, the Financial Accounting Standards Board, ("FASB") issued ASU No. 2013-11, Income Taxes (Topic 740): Presentation of an Unrecognized Tax Benefit When a Net Operating Loss Carryforward, a Similar Tax Loss, or a Tax Credit Carryforward Exists. ASU 2011-13 requires presenting unrecognized tax benefits netted against deferred tax assets if such assets are sufficient and expected to replace cash payment, should an uncertain tax position not be sustained. This update is effective for annual periods beginning on or after December 15, 2013, and interim periods within those annual periods. Entities can choose to apply the update retrospectively. Management has not adopted this update early and continues to evaluate it’s effect on the Company's condensed consolidated financial statements in anticipation of the effective date.
	In February 2013, the issued Accounting Standards Update (“ASU”) No. 2013-02, Reporting of Amounts Reclassified Out of Accumulated Other Comprehensive Income. This guidance requires an entity to present information about significant items reclassified out of Accumulated Other Comprehensive Income (AOCI) by component and for items reclassified out of AOCI and into net income, an entity must disclose the effect of such items on the affected net income line item. ASU No. 2013-02 is effective for annual periods beginning on or after December 15, 2012 and interim periods within those annual periods and must be applied retrospectively. The adoption of ASU 2013-02 had no impact on the Company's condensed consolidated financial statements.
	In December 2011, FASB issued Accounting Standards Update, or ASU 2011-11 Balance Sheet: Disclosures about Offsetting Assets and Liabilities. The new disclosure requirements mandate that entities disclose both gross and net information about instruments and transactions eligible for offset in the statement of financial position, as well as instruments and transactions subject to an agreement similar to a master netting arrangement. In addition, the standard requires disclosure of collateral received and posted in connection with master netting agreements or similar arrangements. This ASU is effective for fiscal years, and interim periods within those years, beginning on or after January 1, 2013. In January 2013, the FASB issued ASU 2013-01 Clarifying the Scope of Disclosures about Offsetting Assets and Liabilities. This update addresses implementation issues of ASU 2011-11. The adoption of ASU 2011-11 and ASU 2013-01 had no impact on the Company’s condensed consolidated statement of operations and comprehensive income and condensed consolidated balance sheet.

ADDITIONAL_FINANCIAL_INFORMATI

ADDITIONAL FINANCIAL INFORMATION	9 Months Ended
	Sep. 30, 2013
Organization, Consolidation and Presentation of Financial Statements [Abstract]	'
ADDITIONAL FINANCIAL INFORMATION	'
	ADDITIONAL FINANCIAL INFORMATION
	Fair Value Measurement
	The following table presents the Company’s assets and liabilities that are measured at fair value on a recurring basis during the period and the related hierarchy levels (amounts in thousands):
		Fair Value Measurements on a Recurring Basis
		as of September 30, 2013
		Level 1			Level 2			Level 3			Total
	Financial Assets/(Liabilities):
	Money market accounts	$	1,058		$	—		$	—		$	1,058
	Open contracts and other positions	—			(10,739		)	—			(10,739		)
	CIBC treasury bills	721			—			—			721
	Certificates of deposit	82			—			—			82
	Investment in gold	133			—			—			133
	Customer and broker open contracts and other positions	—			123,121			—			123,121
	Total	$	1,994		$	112,382		$	—		$	114,376
		Fair Value Measurements on a Recurring Basis
		as of December 31, 2012
		Level 1			Level 2			Level 3			Total
	Financial Assets:
	Money market accounts	$	12,064		$	—		$	—		$	12,064
	Open contracts and other positions	810			—			—			810
	U.S. treasury bills	29,998			—			—			29,998
	CIBC treasury bills	1,355			—			—			1,355
	Certificates of deposit	82			—			—			82
	Investment in gold	168			—			—			168
	Customer and broker open contracts and other positions	74,943			—			—			74,943
	Total	$	119,420		$	—		$	—		$	119,420
	The Company has not changed its valuation techniques in measuring the fair value of any financial assets and liabilities during the period. The Company has included Open contracts and other positions and Customer and broker open contracts and other positions as Level 2 as of September 30, 2013 as these represent the fair value of the derivative contracts which are indexed to securities and commodities with quoted prices in active markets.
	Level 1 Financial Assets
	The Company has money market accounts, certificates of deposit, CIBC treasury bills and an investment in gold that are Level 1 financial instruments that are recorded based upon listed or quoted market rates. The money market accounts are recorded in Cash and cash equivalents and Cash and securities held for customers, the treasury bills are recorded in Cash and cash equivalents and Short term investments, based upon their maturity, the certificates of deposit are recorded in Short term investments and the investment in gold is recorded in Receivables from banks and brokers.
	Level 2 Financial Assets and Liabilities
	The Company has open contracts and other positions that are Level 2 financial instruments that are recorded in Receivables from banks and brokers.
	The Company has customer and broker open contracts and other positions that are Level 2 financial instruments that are recorded in Payable to customers, brokers, dealers, FCMs and other regulated entities.
	These Level 2 financial instruments are based upon directly observable values for underlying instruments.
	Financial Instruments Not Measured at Fair Value
	The table below presents the carrying value, fair value and fair value hierarchy category of certain financial instruments that are not measured at fair value in the Condensed Consolidated Balance Sheet (amounts in thousands). The carrying values of Receivables from banks and brokers not measured at fair value approximate fair value because of the relatively short period of time between their origination and expected maturity. The carrying values of Payables to customers, brokers, dealers, FCMs, and other regulated entities include amounts deposited by these financial institutions in order for the Company to act as a clearing broker. The carrying value of Payables to customers, brokers, dealers, FCMs, and other regulated entities are based on observable market prices and approximate fair value. The carrying value of Loan payable represents the term loan entered into as part of the GFT acquisition (see note 6). The loan is at a market rate and therefore the carrying value is deemed to be the fair value. The carrying value of Accrued expense and other liabilities includes $20.0 million, referred to as the Holdback Amount, to be paid net of an amount required to settle certain liabilities of GFT after the closing date of the acquisition (see note 5). The carrying values of Accrued expense and other liabilities not measured at fair value approximate fair value because of the relatively short period of time between their origination and expected settlement date.
	In April 2011, the Company acquired customer account balances and effective customer agreements from Deutsche Bank AG, relating to Deutsche Bank’s “dbFX” business, for an upfront payment and additional contractual future payments to be made to Deutsche Bank based upon volume generated from the acquired customers over a two-year period following the closing of the acquisition. In accordance with ASC 835-30, Interest, the Company accounted for the payments due to dbFX as a note payable. As such, the total payments due to dbFX under the agreement were discounted to their present value using an imputed rate of interest. This liability was settled during July 2013.
		As of September 30, 2013						Fair Value Measurements using:
		Carrying Value			Fair Value			Quoted Prices		Significant				Significant
								in Active		Observable				Unobservable
								Markets for		Inputs				Inputs
								Identical Assets		(Level 2)				(Level 3)
								(Level 1)
	Financial Assets:
	Receivables from banks and brokers	$	197,044		$	197,044		—		$	197,044			—
	Financial Liabilities:
	Payables to customers, brokers, dealers, FCMs and other regulated entities	807,192			807,192			—		807,192				—
	Loan payable	$	33,200		$	33,200				$	33,200
	Accrued expense and other liabilities	$	20,000		$	20,000				$	20,000
		As of December 31, 2012						Fair Value Measurements using:
		Carrying Value			Fair Value			Quoted Prices		Significant				Significant
								in Active		Observable				Unobservable
								Markets for		Inputs				Inputs
								Identical Assets		(Level 2)				(Level 3)
								(Level 1)
	Financial Assets:
	Receivables from banks and brokers	$	89,106		$	89,106		—		$	89,106			—
	Financial Liabilities:
	Payables to customers, brokers, dealers, FCMs and other regulated entities	$	371,368		$	371,368		—		$	371,368			—
	Payable to dbFX	$	2,386		$	2,392		—		—				$	2,392
	The Company’s investment in Kapitall, Inc., recorded in Other assets, is carried at cost. It is not practical to estimate the fair value of the Kapitall, Inc. stock as Kapitall, Inc. is a privately held company and there is no available market transaction data.
	Receivables from Banks and Brokers
	Amounts receivable from banks and brokers consisted of the following as of (amounts in thousands):
		30-Sep-13			31-Dec-12
Required collateral	$	119,298		$	47,595
Cash in excess of required collateral	77,746			41,343
Open positions	(10,739		)	810
Investment in spot gold	133			168
	$	186,438		$	89,916
The Company has posted funds with banks and brokers as collateral required by agreements for holding trading positions. In addition, the Company has deposited with such banks and brokers cash in excess of required collateral. These amounts are reflected as Receivables from banks and brokers on the Condensed Consolidated Balance Sheets.
Derivatives
The Company's contracts with its customers and its liquidity providers are deemed to be derivative instruments. The table below represents the fair values of the Company’s derivative instruments reported within Receivables from banks and brokers and Payables to customers, brokers, dealers, FCMs and other regulated entities on the accompanying Condensed Consolidated Balance Sheet (amounts in thousands):
	September 30, 2013
	Gross amounts of			Gross amount of			Net amounts of
	assets for			liabilities for			assets/liabilities
	derivative open			derivative open			for derivative
	positions at fair			positions at fair			open positions at
	value			value			fair value
Derivative Instruments:
Foreign currency exchange contracts	$	134,088		$	29,000		$	105,088
CFD contracts	29,595			28,210			1,385
Metals contracts	10,038			4,129			5,909
Total	$	173,721		$	61,339		$	112,382
	September 30, 2013
	Cash Collateral			Net amounts of			Net amounts of
				assets/liabilities			assets/liabilities
				for derivative			presented in the
				open positions at			balance sheet
				fair value
Derivative Assets/Liabilities:
Receivables from bank and brokers	$	197,044		$	(10,739	)	$	186,438
Payables to customers, brokers, dealers, FCMs and other regulated entities	$	807,192		$	123,121		$	684,071
The Company’s derivatives include different contract types, which vary in price. Foreign exchange contracts typically have prices less than two dollars, while certain metals contracts and contracts for difference can be considerably higher priced. The table below represents the notional values of the Company’s derivative instruments reported within Receivables from banks and brokers and Payables to customers, brokers, dealers, FCMs and other regulated entities on the accompanying Condensed Consolidated Balance Sheet (amounts in millions):
	September 30, 2013
	Notional amounts			Notional amounts
	of derivative open			of derivative open
	long positions			short positions
Derivative Instruments:
Foreign currency exchange contracts	$	2,805		$	3,713
CFD contracts	331			62
Metals contracts	1			—
Total	$	3,137		$	3,775
The Company did not designate any of its derivatives as hedging instruments. Net gains/(losses) with respect to derivative instruments reflected in Trading Revenue in the accompanying Condensed Consolidated Statements of Operations and Comprehensive Income for the nine months ended September 30, 2013 were as follows (amounts in thousands):
Derivative Instruments:
Foreign currency exchange contracts	$	88,111
CFD contracts	11,324
Metals contracts	44,273
Total	$	143,708
Property and Equipment
Property and equipment, including leasehold improvements and capitalized software development costs, consisted of the following as of (amounts in thousands):
	30-Sep-13			31-Dec-12
Software	$	24,157		$	19,757
Computer equipment	6,634			5,248
Leasehold improvements	6,518			1,863
Telephone equipment	725			725
Office equipment	1,944			1,471
Furniture and fixtures	1,107			241
Web site development costs	654			654
	41,739			29,959
Less: Accumulated depreciation and amortization	(23,108		)	(18,936		)
Property and equipment, net	$	18,631		$	11,023
As mentioned in Note 1 above, in September 2013, the Company purchased all of the outstanding share capital of GFT. The allocation of the preliminary purchase price to property and equipment is detailed below in Note 5, “Acquisition”.
Depreciation and amortization expense for property and equipment was $1.9 million and $1.1 million for the three months ended September 30, 2013 and 2012, respectively, and $5.2 million and $3.2 million for the nine months ended September 30, 2013 and 2012, respectively.
Intangible Assets
The Company's various finite-lived intangible assets consisted of the following as of (amounts in thousands):
	30-Sep-13						31-Dec-12
	Cost			Accumulated			Cost			Accumulated
				Amortization						Amortization
Customer list	$	21,974		$	(13,237	)	$	19,356		$	(12,138	)
Technology	26,860			(352		)	1,560			(37		)
Trademark	750			(14		)	430			(14		)
Non-compete agreement	—			—			1,859			(1,510		)
	$	49,584		$	(13,603	)	$	23,205		$	(13,699	)
As mentioned in Note 1 above, in September 2013, the Company purchased all of the outstanding share capital of GFT. The allocation of the preliminary purchase price to intangible assets is detailed below in Note 5, “Acquisition”.
In 2003, the Company acquired the Forex.com domain name for $0.3 million, and in 2004, the foreignexchange.com domain name was purchased for $0.1 million. Because the rights to use these domain names require the payment of a nominal annual renewal fee, management determined that there was no legal, regulatory or technological limitation on their useful lives. Accordingly, these indefinite-lived assets are not amortized. In accordance with ASC 350-10, the Company tests intangible assets for impairment on an annual basis in the fourth quarter and on an interim basis when conditions indicate impairment may have occurred.
Amortization expense for the purchased intangibles was $0.5 million and $0.6 million for the three months ended September 30, 2013 and 2012, respectively and $1.7 million and $3.4 million for the nine months ended September 30, 2013 and 2012, respectively. Intangibles arising on the GFT acquisition contributed seven days of amortization expense amounting to $0.1 million.
Goodwill
Goodwill is calculated as the difference between the cost of acquisition and the fair value of the net identifiable assets of an acquired business. As of September 30, 2013 and December 31, 2012, the Company had recorded goodwill of approximately $11.4 million and $9.0 million, respectively.
Goodwill increased $1.7 million as a result of the acquisition of GFT. In addition, during the nine months ended September 30, 2013, the finalization of the fair value of assets acquired as a result of the OEC acquisition in 2012 resulted in an increase of $0.7 million to goodwill.
Other Assets
Other assets consisted of the following as of (amounts in thousands):
	30-Sep-13			31-Dec-12
Vendor and security deposits	$	3,508		$	3,647
Current tax receivable	7,125			5,549
Deferred tax assets	3,338			4,968
Investment in Kapitall, Inc.	500			500
Indemnification asset	12,077			—
Miscellaneous receivables	8,422			2,489
	$	34,970		$	17,153
The Company has recorded a liability of $12.3 million in Accrued expenses and other liabilities. This represents the Company's best estimate for the settlement of certain liabilities that were incurred as a result of ordinary course of operations in GFT prior to its acquisition. The actual amount required to settle these liabilities may vary from this estimate.
Under the terms of the acquisition of GFT, the selling stockholder of GFT has agreed to indemnify the Company for these liabilities that are expected to be settled after September 24, 2013. Based on the Company's best estimate of the amounts necessary to settle such liabilities, the Company recorded an indemnification asset of $12.1 million at September 30, 2013. This is included within Other current assets in the preliminary purchase price allocation of GFT, refer to note 5.

RELATED_PARTY_TRANSACTIONS

RELATED PARTY TRANSACTIONS	9 Months Ended
	Sep. 30, 2013
Related Party Transactions [Abstract]	'
RELATED PARTY TRANSACTIONS	'
	RELATED PARTY TRANSACTIONS
	Certain officers and directors of the Company have personal funds on deposit in customer accounts with the Company, which are recorded in Payables to customers, brokers, dealers, FCMs and other regulated entities on the Condensed Consolidated Balance Sheets. The aggregate amount of these funds was $2.6 million and $2.4 million at September 30, 2013 and December 31, 2012, respectively.
	Scivantage, Inc. provides hosting services to GAIN Capital Securities, Inc., (“GCSI”) under a one-year agreement dated December 1, 2010, which automatically renews for successive one-year terms, in which Scivantage provides the technology infrastructure hosting facility for GCSI, who provides brokerage securities services. Two members of the Company’s board of directors, Messrs. Calhoun and Sugden, are members of the board of directors of Scivantage.

ACQUISITION

ACQUISITION	9 Months Ended
	Sep. 30, 2013
Business Combinations [Abstract]	'
ACQUISITION	'
	ACQUISITIONS
	Global Futures & Forex, Ltd
	On September 24, 2013, GAIN Capital Holdings, Inc., entered into an Amended and Restated Stock Purchase Agreement with Gary L. Tilkin, a natural person (the “Seller”), and GFT, pursuant to which the Company purchased all of the issued and outstanding share capital of GFT from the Seller. The acquisition was made as part of the Company's strategy to increase its offering of products and to expand its retail and institutional businesses into new markets and geographies.
	The preliminary purchase price of GFT was derived as follows (amounts in thousands):
	Cash	$	40,000
	Loan payable	33,200
	Common Stock issued	35,079
	Total purchase price	$	108,279
	The preliminary purchase price of GFT was allocated to the fair value of various assets and liabilities as follows (amounts in thousands):
	Cash and cash equivalents acquired	$	15,781
	Cash and cash equivalents held for customers acquired	228,419
	Receivable from brokers	61,028
	Property and equipment	7,515
	Other current assets	18,928
	Total tangible assets	331,671
	Total liabilities assumed	253,558
	Net assets	78,113
	Consideration less net assets	30,165
	Identifiable intangible assets:
	Software	25,300
	Customer relationships	3,150
	Intangible assets, net	28,450
	Goodwill	1,715
	The foregoing purchase price allocation is preliminary. This is due to the proximity of the closing date of the acquisition to the period end. The final allocation will be based on final analyses of identifiable intangible assets, property and equipment, contingent liabilities and income taxes and will be finalized after the data necessary to complete the analyses of fair values of assets and liabilities is obtained and analyzed.
	Acquisition expenses of $0.5 million and $1.5 million for the three months ended September 30, 2013 and the nine months ended September 30, 2013 respectively, were incurred. These are recorded in Acquisition expenses.
	For the seven day period from acquisition to September 30, 2013, revenues generated by GFT were $2.8 million and expenses were $2.1 million generating a profit before taxes of $0.7 million.
	OEC
	On June 27, 2012, Group, LLC and optionsXpress Holdings, Inc., a subsidiary of The Charles Schwab Corporation, entered into a Stock Purchase Agreement whereby the Company acquired Paragon Futures Group, Inc., which owned all membership interests of OEC, an online futures broker, for a purchase price of $12.0 million. This acquisition was made as part of the Company’s plan to offer additional products to its customers and diversify its revenue streams. The transaction was completed on August 31, 2012. In addition to the $12.0 million paid at the closing, there was an additional payment made in the fourth quarter of 2012 of $2.7 million based on a contractual working capital adjustment.
	The purchase price of OEC was derived as follows (amounts in thousands):
	Cash paid	$	12,000
	Working capital adjustment	2,691
	Total purchase price	$	14,691
	The purchase price of OEC was allocated to the fair value of various assets and liabilities as follows (amounts in thousands):
	Cash and cash equivalents acquired	$	5,187
	Cash and securities held for customers acquired	109,042
	Receivables from brokers acquired	815
	Other assets acquired	98
	Total tangible assets acquired	$	115,142
	Total liabilities assumed	(109,960		)
	Identifiable intangible assets:
	Trademark	650
	Technology	1,630
	Customer relationships	630
	Goodwill	6,599
	Acquisition expenses of $0.1 million for the three months ended September 30, 2012 and the nine months ended September 30, 2012 , were incurred. These are recorded in "Acquisition expenses".
	Pro Forma Information:
	The following unaudited pro forma operating data are presented as if the acquisition of GFT had occurred on January 1st of the respective fiscal years for which comparative information is presented. Additionally, the acquisition of OEC (which was consummated in August 2012) is presented as if it had consummated on January 1, 2012 for the purposes of the comparative periods. The unaudited pro forma data does not include the impact of forecasted operating expense synergies
	The unaudited pro forma data is provided for informational purposes only and may not necessarily be indicative of future results of operations or what the results of operations would have been had the Company and GFT and OEC operated as a combined entity for the periods presented.
	Unaudited pro forma income statement line items for the three and nine months ended September 30, 2013 and 2012, were as follows (amounts in thousands):
		For the Three Months Ended September 30,						For the Nine Months Ended September 30,
		2013			2012			2013			2012
	REVENUE:
	Total non-interest revenue	$	81,195		$	66,504		$	270,027		$	203,838
	Interest revenue	215			231			735			838
	Interest Expense	843			724			2,333			2,351
	Total net interest revenue/(expense)	(628		)	(493		)	(1,598		)	(1,513		)
	Net revenue	80,567			66,011			268,429			202,325
	EXPENSES:
	Depreciation and amortization	2,519			2,100			7,536			6,082
	Purchased intangible amortization	1,215			1,444			3,997			6,057
	Acquisition expense	451			85			1,456			85
	Restructuring	439			—			439			634
	Other expense items*	70,902			64,435			230,221			200,559
Total	75,526			68,064			243,649			213,417
INCOME BEFORE INCOME TAX EXPENSE	5,041			(2,053		)	24,780			(11,092		)
Income tax expense	1,890			(770		)	9,293			(4,159		)
Net income / (loss)	$	3,151		$	(1,283	)	$	15,487		$	(6,933	)
* Other expense items for the nine month period ended September 30, 2013 included a one-time, non-recurring expense of $8.8 million relating to a GFT accrual for certain liabilities to third parties.

TERM_LOAN_AND_REVOLVER

TERM LOAN AND REVOLVER	9 Months Ended
	Sep. 30, 2013
Debt Disclosure [Abstract]	'
TERM LOAN AND REVOLVER	'
	TERM LOAN AND REVOLVER
	As part of the acquisition of GFT, the Company's previously outstanding revolving line of credit was repaid in full, and a Loan and Security Agreement was entered into with the selling stockholder of GFT providing for a $33.2 million term loan to the Company. The loan will mature on the date that is five years from September 24, 2013, the closing date of the acquisition, and will bear interest at a rate of 8.0% per annum, payable quarterly. The Company will also make minimum quarterly payments of principal in an amount of $1.5 million per quarter, although no payments, other than scheduled interest payments, are required to be made until 80% of certain assumed liabilities of GFT are settled. Please see "Item 2. Management's Discussion and Analysis of Financial Condition and Results of Operations - Overview - GFT Transaction" for more information about the Loan and Security Agreement.

SHARE_BASED_COMPENSATION

SHARE BASED COMPENSATION	9 Months Ended
	Sep. 30, 2013
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]	'
SHARE BASED COMPENSATION	'
	SHARE BASED COMPENSATION
	During the nine months ended September 30, 2013, 0.8 million shares of restricted stock and approximately 0.5 million options to purchase common stock, valued at $3.6 million and $0.6 million, respectively, were granted to employees and non-employee members of the Board of Directors, compared to 0.6 million shares of restricted stock and 0.3 million options to purchase common stock, valued at $3.1 million and $0.7 million, respectively during the nine months ended September 30, 2012.
	The Company determines the fair value of restricted stock units and awards at the date of grant based on the value of the Company’s common stock. The Company determines the fair value of our stock option awards at the date of grant using a Black-Scholes valuation model. This model requires assumptions and judgments on the expected volatility, dividend yield, the risk-free interest rate and the expected term of the stock options. The following assumptions were used for stock options granted in the period:
		For the Nine Months Ended September 30,
		2013	2012
	Valuation Assumptions
	Risk-free rate	0.80%	0.90%
	Expected volatility	48.80%	48.50%
	Expected term (years)	4.75	4.75
	Dividend yield	4.90%	—%

EARNINGS_PER_COMMON_SHARE

EARNINGS PER COMMON SHARE	9 Months Ended
	Sep. 30, 2013
Earnings Per Share [Abstract]	'
EARNINGS PER COMMON SHARE	'
	EARNINGS PER COMMON SHARE
	Basic and diluted earnings per common share are computed by dividing net income by the weighted average number of common shares outstanding during the period. Diluted earnings per share includes the determinants of basic net income per share and, in addition, gives effect to the potential dilution that would occur if securities or other contracts to issue common stock were exercised, vested or converted into common stock, unless they are anti-dilutive. Diluted weighted average common shares include vested and unvested stock options, vested restricted stock units which are to be delivered as soon as administratively practicable on or after December 31, 2014, unvested restricted stock units and unvested restricted stock awards. Approximately 0.6 million and 0.3 million stock options were excluded from the calculation of diluted earnings per share for the nine months ended September 30, 2013 and the nine months ended September 30, 2012, respectively, as they were anti-dilutive.
	The following table sets forth the computation of earnings per share (amounts in thousands except share and per share data):
		For the Three Months Ended September 30,				For the Nine Months Ended September 30,
		2013		2012		2013		2012
	Net income applicable to GAIN Capital Holdings, Inc.	$	5,600	$	3,221	$	27,044	$	6,409
	Adjustment(1)	—		—		154		—
	Net income applicable to GAIN common shareholders	$	5,600	$	3,221	$	26,890	$	6,409
	Weighted average common shares outstanding:
	Basic weighted average common shares outstanding	36,062,659		35,250,404		35,563,701		34,893,622
	Effect of dilutive securities:
	Stock options	1,620,851		1,382,802		1,244,009		1,764,568
	RSUs/RSAs	2,047,347		1,927,451		1,914,957		2,269,483
	Diluted weighted average common shares outstanding	39,730,857		38,560,657		38,722,667		38,927,673
	Earnings per common share
	Basic	$	0.16	$	0.09	$	0.76	$	0.18
	Diluted	$	0.14	$	0.08	$	0.69	$	0.16
	-1	During the period an adjustment to retained earnings was made, reflecting the amounts deemed uncollectible associated with previously issued preferred stock, which was converted to common stock immediately prior to the IPO.

LEGAL

LEGAL	9 Months Ended
	Sep. 30, 2013
Commitments and Contingencies Disclosure [Abstract]	'
LEGAL	'
	LEGAL
	From time to time the Company becomes involved in legal proceedings and in each case the Company assesses the likely liability and/or the amount of damages as appropriate. Where available information indicates that it is probable a liability had been incurred at the date of the condensed consolidated financial statements and the Company can reasonably estimate the amount of that loss, the Company accrues the estimated loss by a charge to income. In many proceedings, however, it is inherently difficult to determine whether any loss is probable or even possible or to estimate the amount of any loss. In addition, even where loss is possible or an exposure to loss exists in excess of the liability already accrued with respect to a previously recognized loss contingency, it is often not possible to reasonably estimate the size of the possible loss or range of loss.
	For certain legal proceedings, the Company can estimate possible losses, additional losses, ranges of loss or ranges of additional loss in excess of amounts accrued. For certain other legal proceedings, the Company cannot reasonably estimate such losses, if any, since the Company cannot predict if, how or when such proceedings will be resolved or what the eventual settlement, fine, penalty or other relief, if any, may be, particularly for proceedings that are in their early stages of development or where plaintiffs seek substantial or indeterminate damages. Numerous issues must be developed, including the need to discover and determine important factual matters and the need to address novel or unsettled legal questions relevant to the proceedings in question, before a loss or additional loss or range of loss or additional loss can be reasonably estimated for any proceeding.
	Litigation
	On February 16, 2012, the Company received a Letter of Claim on behalf of certain individuals who had lost money in an investment scheme operated by a third-party money management firm, incorporated in the United Kingdom, which has since been closed down by the United Kingdom’s Financial Services Authority. The investment firm, Cameron Farley Ltd, had opened a corporate account with the Company and invested the individuals’ money, representing such funds as its own, while operating a fraudulent scheme. Though a complaint has been filed and served on the Company, the claimants requested, and the Company agreed, to follow the United Kingdom’s Pre-Action Protocol, a pre-litigation process intended to resolve matters without the need to engage in formal litigation. The Company submitted a Response to the Letter before Claim on July 4, 2012. On July 5, 2012 the Company received a substantially similar Letter of Claim on behalf of further individuals. Subsequently, the parties agreed to consolidate claims by those other similarly situated individuals with the pending Pre-Action Protocol process. The parties agreed it would be more appropriate for the proceedings to be dealt with in the Commercial Court and the matters were transferred pursuant to Consent Orders dated March 14, 2013. The Company subsequently filed an application for strike out and/or summary judgment in respect of all claims on March 15, 2013. The claimants filed an answer to the Company's motion on June 2, 2013 and subsequently the Company filed a response to this answer on July 15, 2013. A hearing was held on the Company's application for strike out and/or summary judgment on September 18 and 19, 2013.  After the hearing, the judge asked the claimants to respond in writing to his additional questions from the hearing.  The complaints had until October 11, 2013 to provide answers and the Company was given until November 1, 2013 to respond.  The Company is now waiting for the judge’s ruling on the motion.  The Company can provide no assurances that this matter will be successfully resolved. This matter is currently pending. At this time, a potential loss or a potential range of loss cannot be reasonably estimated.
	Through the Company’s acquisition of OEC, the Company became the subject of a patent infringement lawsuit originally filed against OEC on February 9, 2010 in the U.S. District Court for the Northern District of Illinois by Trading Technologies International, Inc. seeking injunctive relief and unspecified damages. As reflected in a Second Amended Complaint filed on June 15, 2011, plaintiff alleges infringement of 12 patents relating to real-time display of price quotes and market depth on OEC’s electronic trading interfaces. The case was consolidated with 11 related cases in February 2011, and the parties have exchanged infringement, non-infringement and invalidity contentions for several of the disputed patents. In June 2011 the court stayed discovery to allow summary judgment briefing on the ramifications of a recent Federal Circuit decision. On February 9, 2012, the court issued an order, which granted OEC’s motions for summary judgment, resulting in a substantial narrowing of the scope of plaintiff’s claims. Plaintiff filed a motion for reconsideration of that ruling on March 8, 2012. Plaintiff also filed a motion for certification of judgment for interlocutory appeal. The court denied plaintiff’s motion for reconsideration but granted plaintiff’s motion for certification of judgments of patent invalidity with respect to four of the asserted patents. On August 30, 2013, the Federal Circuit issued its opinion vacating the district court’s judgment of patent invalidity regarding four of the asserted patents.  On September 30, 2013, certain of the appellees filed a petition for rehearing and rehearing en banc with the Federal Circuit.  Since the district court’s certification of judgments ruling, the court has continued its stay of discovery. Plaintiff’s complaint does not specify the amount of damages sought. At this time, a potential loss or a potential range of loss cannot be reasonably estimated.

INCOME_TAXES

INCOME TAXES	9 Months Ended
	Sep. 30, 2013
Income Tax Disclosure [Abstract]	'
INCOME TAXES	'
	INCOME TAXES
	The Company’s provision for income taxes was approximately $3.0 million and $1.2 million for the three months ended September 30, 2013 and the three months ended September 30, 2012, respectively. These amounts reflect effective tax rates of 35.2% and 27.3%, respectively.
	The Company’s provision for income taxes for the nine months ended September 30, 2013 and the nine months ended September 30, 2012 was $11.2 million and $2.2 million respectively.
	The Company’s effective tax rates of 29.2% and 25.1% for the nine months ended September 30, 2013 and the nine months ended September 30, 2012, respectively, reflect the Company’s estimate of the annual effective tax rate, adjusted for certain discrete items. The primary reason for the difference in the effective tax rate for the nine months ended September 30, 2013 compared to the U.S. federal statutory income tax rate is due to the mix of earnings across foreign jurisdictions.
	Deferred income taxes reflect the net tax effects of temporary differences between the financial reporting and tax basis of assets and liabilities and are measured using the enacted tax rates and laws that will be in effect when such differences are expected to reverse. The Company’s net deferred tax assets are included in Other assets on the Condensed Consolidated Balance Sheet.

REGULATORY_REQUIREMENTS

REGULATORY REQUIREMENTS	9 Months Ended
	Sep. 30, 2013
Banking and Thrift [Abstract]	'
REGULATORY REQUIREMENTS	'
	REGULATORY REQUIREMENTS
	The following table illustrates the minimum regulatory capital our subsidiaries were required to maintain as of September 30, 2013 and the actual amounts of capital that were maintained (amounts in millions):
	Entity Name	Minimum		Capital		Excess		Percent  of
		Regulatory		Levels		Net		Requirement
		Capital		Maintained		Capital		Maintained
		Requirements
	GFT Global Markets UK Ltd.	$	40.4	$	51.9	$	11.5	128	%
	GAIN Capital Group, LLC	24.8		44.1		19.3		178	%
	GAIN Capital-Forex.com U.K., Ltd.	20.9		50.5		29.6		242	%
	Forex.com Japan Co., Ltd.	3.5		10.8		7.3		309	%
	GAIN Capital-Forex.com Hong Kong, Ltd.	1.9		3.8		1.9		200	%
	GFT Global Markets Asia Pte., Ltd.	1.6		1.8		0.2		113	%
	Global Futures & Forex, Ltd.	1		1.6		0.6		160	%
	GAIN Capital Forex.com Australia, Pty. Ltd.	0.4		2.7		2.3		675	%
	GAIN Capital-Forex.com Canada Ltd.	0.2		1.9		1.7		950	%
	GAIN Capital Securities, Inc.	0.1		0.2		0.1		200	%
	GAIN Global Markets, Inc.	0.1		0.3		0.2		300	%
	Total	$	94.9	$	169.6	$	74.7	179	%
	Regulatory requirements have remained substantially the same as those disclosed in the Company’s Annual Report on Form 10-K filed with the SEC on March 18, 2013 with the exception of the requirements of GAIN Capital Forex.com Australia, Pty. Ltd. (“GCAU”). GCAU holds an Australian Financial Services License issued by the Australian Securities & Investments Commission (“ASIC”). As of January 31, 2013, the ASIC implemented changes to the Regulatory Guide 166. As a result of these changes, GCAU is required to maintain a minimum capital requirement of $0.5 million (AUD 0.5 million) or 5% of the average revenue. This change did not have a material impact on the Company or GCAU.

SEGMENT_INFORMATION

SEGMENT INFORMATION	9 Months Ended
	Sep. 30, 2013
Segment Reporting [Abstract]	'
SEGMENT INFORMATION	'
	SEGMENT INFORMATION
	ASC 280, Disclosures about Segments of an Enterprise and Related Information, establishes standards for reporting information about operating segments. Operating segments are defined as components of an enterprise about which separate financial information is available that is evaluated regularly by the chief operating decision-maker, or decision making group, in deciding how to allocate resources and in assessing performance. Reportable segments are defined as an operating segment that either (a) exceeds 10% of revenue, or (b) reported profit or loss in absolute amount exceeds 10% of profit of all operating segments that did not report a loss or (c) exceeds 10% of the combined assets of all operating segments. The Company’s operations relate to global trading services and solutions. Based on the Company’s management strategies, and common production, marketing, development and client coverage teams, the Company has concluded that it operates in a single operating segment.
	For the nine months ended September 30, 2013 and the nine months ended September 30, 2012, no single customer accounted for more than 10% of the Company’s trading revenue. Although the Company allocates revenue to geographic regions for income tax purposes, the Company does not utilize this method for operational or internal reporting purposes and therefore the Company has no geographic regions for segment reporting.

SUBSEQUENT_EVENTS

SUBSEQUENT EVENTS	9 Months Ended
	Sep. 30, 2013
Subsequent Events [Abstract]	'
SUBSEQUENT EVENTS	'
	SUBSEQUENT EVENTS
	The Company has evaluated events subsequent to September 30, 2013 to assess the need for potential recognition or disclosure in these consolidated financial statements. Such events were evaluated through November 12, 2013, the date these consolidated financial statements were issued.
	In October 2013, the Company announced the payment of a $0.05 dividend per share of Common Stock payable on December 20, 2013 to stockholders of record on December 12, 2013.
	In July 2013, GAIN Securities, an indirect wholly-owned subsidiary of the Company that principally offers equity products, entered into an agreement to transfer substantially all of its customer accounts to TradeKing, LLC. This transaction closed in October 2013.

ADDITIONAL_FINANCIAL_INFORMATI1

ADDITIONAL FINANCIAL INFORMATION (Tables)	9 Months Ended
	Sep. 30, 2013
Organization, Consolidation and Presentation of Financial Statements [Abstract]	'
Assets and Liabilities Measured at Fair Value on Recurring Basis	'
	The following table presents the Company’s assets and liabilities that are measured at fair value on a recurring basis during the period and the related hierarchy levels (amounts in thousands):
		Fair Value Measurements on a Recurring Basis
		as of September 30, 2013
		Level 1			Level 2			Level 3			Total
	Financial Assets/(Liabilities):
	Money market accounts	$	1,058		$	—		$	—		$	1,058
	Open contracts and other positions	—			(10,739		)	—			(10,739		)
	CIBC treasury bills	721			—			—			721
	Certificates of deposit	82			—			—			82
	Investment in gold	133			—			—			133
	Customer and broker open contracts and other positions	—			123,121			—			123,121
	Total	$	1,994		$	112,382		$	—		$	114,376
		Fair Value Measurements on a Recurring Basis
		as of December 31, 2012
		Level 1			Level 2			Level 3			Total
	Financial Assets:
	Money market accounts	$	12,064		$	—		$	—		$	12,064
	Open contracts and other positions	810			—			—			810
	U.S. treasury bills	29,998			—			—			29,998
	CIBC treasury bills	1,355			—			—			1,355
	Certificates of deposit	82			—			—			82
	Investment in gold	168			—			—			168
	Customer and broker open contracts and other positions	74,943			—			—			74,943
	Total	$	119,420		$	—		$	—		$	119,420
Carrying Value and Fair Value and Fair Value Hierarchy Category of Financial Instruments Not Measured at Fair Value in Condensed Consolidated Statements of Financial Condition	'
		As of September 30, 2013						Fair Value Measurements using:
		Carrying Value			Fair Value			Quoted Prices		Significant				Significant
								in Active		Observable				Unobservable
								Markets for		Inputs				Inputs
								Identical Assets		(Level 2)				(Level 3)
								(Level 1)
	Financial Assets:
	Receivables from banks and brokers	$	197,044		$	197,044		—		$	197,044			—
	Financial Liabilities:
	Payables to customers, brokers, dealers, FCMs and other regulated entities	807,192			807,192			—		807,192				—
	Loan payable	$	33,200		$	33,200				$	33,200
	Accrued expense and other liabilities	$	20,000		$	20,000				$	20,000
		As of December 31, 2012						Fair Value Measurements using:
		Carrying Value			Fair Value			Quoted Prices		Significant				Significant
								in Active		Observable				Unobservable
								Markets for		Inputs				Inputs
								Identical Assets		(Level 2)				(Level 3)
								(Level 1)
	Financial Assets:
	Receivables from banks and brokers	$	89,106		$	89,106		—		$	89,106			—
	Financial Liabilities:
	Payables to customers, brokers, dealers, FCMs and other regulated entities	$	371,368		$	371,368		—		$	371,368			—
	Payable to dbFX	$	2,386		$	2,392		—		—				$	2,392
Receivable from Brokers	'
	Amounts receivable from banks and brokers consisted of the following as of (amounts in thousands):
		30-Sep-13			31-Dec-12
	Required collateral	$	119,298		$	47,595
	Cash in excess of required collateral	77,746			41,343
	Open positions	(10,739		)	810
	Investment in spot gold	133			168
		$	186,438		$	89,916
Fair Values of Derivative Instruments	'
	The table below represents the fair values of the Company’s derivative instruments reported within Receivables from banks and brokers and Payables to customers, brokers, dealers, FCMs and other regulated entities on the accompanying Condensed Consolidated Balance Sheet (amounts in thousands):
		September 30, 2013
		Gross amounts of			Gross amount of			Net amounts of
		assets for			liabilities for			assets/liabilities
		derivative open			derivative open			for derivative
		positions at fair			positions at fair			open positions at
		value			value			fair value
	Derivative Instruments:
	Foreign currency exchange contracts	$	134,088		$	29,000		$	105,088
	CFD contracts	29,595			28,210			1,385
	Metals contracts	10,038			4,129			5,909
	Total	$	173,721		$	61,339		$	112,382
		September 30, 2013
		Cash Collateral			Net amounts of			Net amounts of
					assets/liabilities			assets/liabilities
					for derivative			presented in the
					open positions at			balance sheet
					fair value
	Derivative Assets/Liabilities:
	Receivables from bank and brokers	$	197,044		$	(10,739	)	$	186,438
	Payables to customers, brokers, dealers, FCMs and other regulated entities	$	807,192		$	123,121		$	684,071
Notional Values of Derivative Instruments	'
	The Company’s derivatives include different contract types, which vary in price. Foreign exchange contracts typically have prices less than two dollars, while certain metals contracts and contracts for difference can be considerably higher priced. The table below represents the notional values of the Company’s derivative instruments reported within Receivables from banks and brokers and Payables to customers, brokers, dealers, FCMs and other regulated entities on the accompanying Condensed Consolidated Balance Sheet (amounts in millions):
		September 30, 2013
		Notional amounts			Notional amounts
		of derivative open			of derivative open
		long positions			short positions
	Derivative Instruments:
	Foreign currency exchange contracts	$	2,805		$	3,713
	CFD contracts	331			62
	Metals contracts	1			—
	Total	$	3,137		$	3,775
Net Gains (Losses) With Respect to Derivative Instruments Which are Reflected in Trading Revenue	'
	Net gains/(losses) with respect to derivative instruments reflected in Trading Revenue in the accompanying Condensed Consolidated Statements of Operations and Comprehensive Income for the nine months ended September 30, 2013 were as follows (amounts in thousands):
	Derivative Instruments:
	Foreign currency exchange contracts	$	88,111
	CFD contracts	11,324
	Metals contracts	44,273
	Total	$	143,708
Property and Equipment Including Leasehold Improvements and Capitalized Software Development Costs	'
	Property and equipment, including leasehold improvements and capitalized software development costs, consisted of the following as of (amounts in thousands):
		30-Sep-13			31-Dec-12
	Software	$	24,157		$	19,757
	Computer equipment	6,634			5,248
	Leasehold improvements	6,518			1,863
	Telephone equipment	725			725
	Office equipment	1,944			1,471
	Furniture and fixtures	1,107			241
	Web site development costs	654			654
		41,739			29,959
	Less: Accumulated depreciation and amortization	(23,108		)	(18,936		)
	Property and equipment, net	$	18,631		$	11,023
Intangible Assets	'
	The Company's various finite-lived intangible assets consisted of the following as of (amounts in thousands):
		30-Sep-13						31-Dec-12
		Cost			Accumulated			Cost			Accumulated
					Amortization						Amortization
	Customer list	$	21,974		$	(13,237	)	$	19,356		$	(12,138	)
	Technology	26,860			(352		)	1,560			(37		)
	Trademark	750			(14		)	430			(14		)
	Non-compete agreement	—			—			1,859			(1,510		)
		$	49,584		$	(13,603	)	$	23,205		$	(13,699	)
Other Assets	'
	Other assets consisted of the following as of (amounts in thousands):
		30-Sep-13			31-Dec-12
	Vendor and security deposits	$	3,508		$	3,647
	Current tax receivable	7,125			5,549
	Deferred tax assets	3,338			4,968
	Investment in Kapitall, Inc.	500			500
	Indemnification asset	12,077			—
	Miscellaneous receivables	8,422			2,489
		$	34,970		$	17,153

ACQUISITION_Tables

ACQUISITION (Tables)	9 Months Ended
	Sep. 30, 2013
Business Combinations [Abstract]	'
Schedule of Purchase Price	'
	Cash	$	40,000
	Loan payable	33,200
	Common Stock issued	35,079
	Total purchase price	$	108,279
	The purchase price of OEC was derived as follows (amounts in thousands):
	Cash paid	$	12,000
	Working capital adjustment	2,691
	Total purchase price	$	14,691
Allocation of Purchase Price to Fair Value of Assets and Liabilities	'
	Cash and cash equivalents acquired	$	15,781
	Cash and cash equivalents held for customers acquired	228,419
	Receivable from brokers	61,028
	Property and equipment	7,515
	Other current assets	18,928
	Total tangible assets	331,671
	Total liabilities assumed	253,558
	Net assets	78,113
	Consideration less net assets	30,165
	Identifiable intangible assets:
	Software	25,300
	Customer relationships	3,150
	Intangible assets, net	28,450
	Goodwill	1,715
	The purchase price of OEC was allocated to the fair value of various assets and liabilities as follows (amounts in thousands):
	Cash and cash equivalents acquired	$	5,187
	Cash and securities held for customers acquired	109,042
	Receivables from brokers acquired	815
	Other assets acquired	98
	Total tangible assets acquired	$	115,142
	Total liabilities assumed	(109,960		)
	Identifiable intangible assets:
	Trademark	650
	Technology	1,630
	Customer relationships	630
	Goodwill	6,599

ACQUISITION_Pro_Forma_Tables

ACQUISITION Pro Forma (Tables)	3 Months Ended													9 Months Ended
	Sep. 30, 2013													Sep. 30, 2013
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]	'													'
Business Acquisition, Pro Forma Information [Table Text Block]	'													'
		For the Three Months Ended September 30,						For the Nine Months Ended September 30,
		2013			2012			2013			2012
	REVENUE:
	Total non-interest revenue	$	81,195		$	66,504		$	270,027		$	203,838
	Interest revenue	215			231			735			838
	Interest Expense	843			724			2,333			2,351
	Total net interest revenue/(expense)	(628		)	(493		)	(1,598		)	(1,513		)
	Net revenue	80,567			66,011			268,429			202,325
	EXPENSES:
	Depreciation and amortization	2,519			2,100			7,536			6,082
	Purchased intangible amortization	1,215			1,444			3,997			6,057
	Acquisition expense	451			85			1,456			85
	Restructuring	439			—			439			634
	Other expense items*	70,902			64,435			230,221			200,559
	Total	75,526			68,064			243,649			213,417
	INCOME BEFORE INCOME TAX EXPENSE	5,041			(2,053		)	24,780			(11,092		)
	Income tax expense	1,890			(770		)	9,293			(4,159		)
	Net income / (loss)	$	3,151		$	(1,283	)	$	15,487		$	(6,933	)
	* Other expense items for the nine month period ended September 30, 2013 included a one-time, non-recurring expense of $8.8 million relating to a GFT accrual for certain liabilities to third parties.

SHARE_BASED_COMPENSATION_Table

SHARE BASED COMPENSATION (Tables)	9 Months Ended
	Sep. 30, 2013
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]	'
Assumptions for Stock Options Granted	'
	The following assumptions were used for stock options granted in the period:
		For the Nine Months Ended September 30,
		2013	2012
	Valuation Assumptions
	Risk-free rate	0.80%	0.90%
	Expected volatility	48.80%	48.50%
	Expected term (years)	4.75	4.75
	Dividend yield	4.90%	—%

EARNINGS_PER_COMMON_SHARE_Tabl

EARNINGS PER COMMON SHARE (Tables)	9 Months Ended
	Sep. 30, 2013
Earnings Per Share [Abstract]	'
Computation of Earnings Per Share	'
	The following table sets forth the computation of earnings per share (amounts in thousands except share and per share data):
		For the Three Months Ended September 30,				For the Nine Months Ended September 30,
		2013		2012		2013		2012
	Net income applicable to GAIN Capital Holdings, Inc.	$	5,600	$	3,221	$	27,044	$	6,409
	Adjustment(1)	—		—		154		—
	Net income applicable to GAIN common shareholders	$	5,600	$	3,221	$	26,890	$	6,409
	Weighted average common shares outstanding:
	Basic weighted average common shares outstanding	36,062,659		35,250,404		35,563,701		34,893,622
	Effect of dilutive securities:
	Stock options	1,620,851		1,382,802		1,244,009		1,764,568
	RSUs/RSAs	2,047,347		1,927,451		1,914,957		2,269,483
	Diluted weighted average common shares outstanding	39,730,857		38,560,657		38,722,667		38,927,673
	Earnings per common share
	Basic	$	0.16	$	0.09	$	0.76	$	0.18
	Diluted	$	0.14	$	0.08	$	0.69	$	0.16
	-1	During the period an adjustment to retained earnings was made, reflecting the amounts deemed uncollectible associated with previously issued preferred stock, which was converted to common stock immediately prior to the IPO.

REGULATORY_REQUIREMENTS_Tables

REGULATORY REQUIREMENTS (Tables)	9 Months Ended
	Sep. 30, 2013
Banking and Thrift [Abstract]	'
Minimum Regulatory Capital Subsidiaries Required to Maintain	'
	The following table illustrates the minimum regulatory capital our subsidiaries were required to maintain as of September 30, 2013 and the actual amounts of capital that were maintained (amounts in millions):
	Entity Name	Minimum		Capital		Excess		Percent  of
		Regulatory		Levels		Net		Requirement
		Capital		Maintained		Capital		Maintained
		Requirements
	GFT Global Markets UK Ltd.	$	40.4	$	51.9	$	11.5	128	%
	GAIN Capital Group, LLC	24.8		44.1		19.3		178	%
	GAIN Capital-Forex.com U.K., Ltd.	20.9		50.5		29.6		242	%
	Forex.com Japan Co., Ltd.	3.5		10.8		7.3		309	%
	GAIN Capital-Forex.com Hong Kong, Ltd.	1.9		3.8		1.9		200	%
	GFT Global Markets Asia Pte., Ltd.	1.6		1.8		0.2		113	%
	Global Futures & Forex, Ltd.	1		1.6		0.6		160	%
	GAIN Capital Forex.com Australia, Pty. Ltd.	0.4		2.7		2.3		675	%
	GAIN Capital-Forex.com Canada Ltd.	0.2		1.9		1.7		950	%
	GAIN Capital Securities, Inc.	0.1		0.2		0.1		200	%
	GAIN Global Markets, Inc.	0.1		0.3		0.2		300	%
	Total	$	94.9	$	169.6	$	74.7	179	%

DESCRIPTION_OF_BUSINESS_AND_BA1

DESCRIPTION OF BUSINESS AND BASIS OF PRESENTATION - (Detail) (USD $)	9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012
Cash and Cash Equivalents [Line Items]	'	'	'
Other assets, net	$34,970	'	$17,153
Changes in operating assets and liabilities:	'	'	'
Cash and securities held for customers	-13,173	-10,760	'
Cash provided by operating activities	10,370	19,094	'
Effect of exchange rate changes on cash and cash equivalents	-4,226	868	'
INCREASE IN CASH AND CASH EQUIVALENTS	-8,497	-52,570	'
CASH AND CASH EQUIVALENTS-Beginning of period	36,820	60,221	'
CASH AND CASH EQUIVALENTS-End of period	28,323	7,651	'
Retained earnings	106,314	'	84,772
Restated [Member] [Member]	'	'	'
Cash and Cash Equivalents [Line Items]	'	'	'
Other assets, net	'	'	17,153
Accrued Liabilities, Current	'	'	1,481
Changes in operating assets and liabilities:	'	'	'
Retained earnings	84,772	'	'
Previously Reported [Member]	'	'	'
Cash and Cash Equivalents [Line Items]	'	'	'
Other assets, net	'	'	17,804
Accrued Liabilities, Current	'	'	1,275
Revised	'	'	'
Changes in operating assets and liabilities:	'	'	'
CASH AND CASH EQUIVALENTS-Beginning of period	'	'	36,820
CASH AND CASH EQUIVALENTS-End of period	28,323	'	36,820
Previously Reported RE [Member]	'	'	'
Changes in operating assets and liabilities:	'	'	'
Retained earnings	'	$85,629	'

ADDITIONAL_FINANCIAL_INFORMATI2

ADDITIONAL FINANCIAL INFORMATION - Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) (USD $)	Sep. 30, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]	'	'
Assets	$114,376	$119,420
Money market accounts	'	'
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]	'	'
Assets	1,058	12,064
Open contracts and other positions	'	'
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]	'	'
Assets	-10,739	810
U.S. treasury bills	'	'
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]	'	'
Assets	'	29,998
Canadian Imperial Bank of Commerce treasury bills	'	'
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]	'	'
Assets	721	1,355
Certificates of deposit	'	'
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]	'	'
Assets	82	82
Investment in gold	'	'
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]	'	'
Assets	133	168
Customer and broker open contracts and other positions	'	'
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]	'	'
Assets	123,121	74,943
Quoted Prices in Active Markets for Identical Assets (Level 1)	'	'
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]	'	'
Assets	1,994	119,420
Quoted Prices in Active Markets for Identical Assets (Level 1) | Money market accounts	'	'
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]	'	'
Assets	1,058	12,064
Quoted Prices in Active Markets for Identical Assets (Level 1) | Open contracts and other positions	'	'
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]	'	'
Assets	'	810
Quoted Prices in Active Markets for Identical Assets (Level 1) | U.S. treasury bills	'	'
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]	'	'
Assets	'	29,998
Quoted Prices in Active Markets for Identical Assets (Level 1) | Canadian Imperial Bank of Commerce treasury bills	'	'
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]	'	'
Assets	721	1,355
Quoted Prices in Active Markets for Identical Assets (Level 1) | Certificates of deposit	'	'
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]	'	'
Assets	82	82
Quoted Prices in Active Markets for Identical Assets (Level 1) | Investment in gold	'	'
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]	'	'
Assets	133	168
Quoted Prices in Active Markets for Identical Assets (Level 1) | Customer and broker open contracts and other positions	'	'
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]	'	'
Assets	'	74,943
Significant Observable Inputs (Level 2)	'	'
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]	'	'
Assets	112,382	'
Significant Observable Inputs (Level 2) | Open contracts and other positions	'	'
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]	'	'
Assets	-10,739	'
Significant Observable Inputs (Level 2) | Customer and broker open contracts and other positions	'	'
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]	'	'
Assets	$123,121	'

ADDITIONAL_FINANCIAL_INFORMATI3

ADDITIONAL FINANCIAL INFORMATION - Carrying Value and Fair Value and Fair Value Hierarchy Category of Financial Instruments Not Measured at Fair Value in Condensed Consolidated Statements of Financial Condition (Detail) (USD $)	Sep. 30, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified
Financial Assets:	'	'
Receivables from banks and brokers	$186,438	$89,916
Financial Liabilities:	'	'
Payables to customers, brokers, dealers, FCMs and other regulated entities	684,071	446,311
Loan payable	33,200	0
Significant Observable Inputs (Level 2)	'	'
Financial Assets:	'	'
Receivables from banks and brokers	197,044	89,106
Financial Liabilities:	'	'
Payables to customers, brokers, dealers, FCMs and other regulated entities	'	371,368
Loan payable	33,200	'
Accrued Liabilities, Current	20,000	'
Significant Unobservable Inputs (Level 3)	'	'
Financial Liabilities:	'	'
Payable to dbFX	'	2,392
Carrying Value	'	'
Financial Assets:	'	'
Receivables from banks and brokers	197,044	89,106
Financial Liabilities:	'	'
Payables to customers, brokers, dealers, FCMs and other regulated entities	'	371,368
Payable to dbFX	'	2,386
Loan payable	33,200	'
Accrued Liabilities, Current	20,000	'
Fair Value	'	'
Financial Assets:	'	'
Receivables from banks and brokers	197,044	89,106
Financial Liabilities:	'	'
Payables to customers, brokers, dealers, FCMs and other regulated entities	'	371,368
Payable to dbFX	'	2,392
Loan payable	33,200	'
Accrued Liabilities, Current	20,000	'
Derivative Financial Instruments, Liabilities [Member] | Significant Observable Inputs (Level 2)	'	'
Financial Assets:	'	'
Derivative, Collateral, Obligation to Return Cash	$807,192	'

ADDITIONAL_FINANCIAL_INFORMATI4

ADDITIONAL FINANCIAL INFORMATION - Receivable from Brokers (Detail) (USD $)	Sep. 30, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified
Receivables from Brokerage Clients [Line Items]	'	'
Receivable from banks and brokers	$186,438	$89,916
Required collateral	'	'
Receivables from Brokerage Clients [Line Items]	'	'
Receivable from banks and brokers	119,298	47,595
Cash in excess of required collateral	'	'
Receivables from Brokerage Clients [Line Items]	'	'
Receivable from banks and brokers	77,746	41,343
Open Position	'	'
Receivables from Brokerage Clients [Line Items]	'	'
Receivable from banks and brokers	-10,739	810
Investment in spot gold	'	'
Receivables from Brokerage Clients [Line Items]	'	'
Receivable from banks and brokers	$133	$168

ADDITIONAL_FINANCIAL_INFORMATI5

ADDITIONAL FINANCIAL INFORMATION - Fair Values of Derivative Instruments (Detail) (USD $)	Sep. 30, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified
Derivatives, Fair Value [Line Items]	'	'
Gross amounts of assets for derivative open positions at fair value	$173,721	'
Gross amounts of liability for derivative open positions at fair value	61,339	'
Net amounts of assets/liabilities for derivative open positions at fair value	112,382	'
Net amounts of assets/liabilities presented in the balance sheet	186,438	89,916
Net amounts of assets/liabilities presented in the balance sheet	684,071	446,311
Derivative Assets	'	'
Derivatives, Fair Value [Line Items]	'	'
Cash Collateral	197,044	'
Net amounts of assets/liabilities for derivative open positions at fair value	-10,739	'
Net amounts of assets/liabilities presented in the balance sheet	186,438	'
Derivative Liabilities	'	'
Derivatives, Fair Value [Line Items]	'	'
Net amounts of assets/liabilities for derivative open positions at fair value	123,121	'
Foreign currency exchange contracts	'	'
Derivatives, Fair Value [Line Items]	'	'
Gross amounts of assets for derivative open positions at fair value	134,088	'
Gross amounts of liability for derivative open positions at fair value	29,000	'
Net amounts of assets/liabilities for derivative open positions at fair value	105,088	'
CFD contracts	'	'
Derivatives, Fair Value [Line Items]	'	'
Gross amounts of assets for derivative open positions at fair value	29,595	'
Gross amounts of liability for derivative open positions at fair value	28,210	'
Net amounts of assets/liabilities for derivative open positions at fair value	1,385	'
Metal contracts	'	'
Derivatives, Fair Value [Line Items]	'	'
Gross amounts of assets for derivative open positions at fair value	10,038	'
Gross amounts of liability for derivative open positions at fair value	4,129	'
Net amounts of assets/liabilities for derivative open positions at fair value	5,909	'
Fair Value, Inputs, Level 2 [Member]	'	'
Derivatives, Fair Value [Line Items]	'	'
Net amounts of assets/liabilities presented in the balance sheet	197,044	89,106
Net amounts of assets/liabilities presented in the balance sheet	'	371,368
Fair Value, Inputs, Level 2 [Member] | Derivative Liabilities	'	'
Derivatives, Fair Value [Line Items]	'	'
Cash Collateral	$807,192	'

ADDITIONAL_FINANCIAL_INFORMATI6

ADDITIONAL FINANCIAL INFORMATION - Notional Values of Derivative Instruments (Detail) (USD $)	Sep. 30, 2013
In Millions, unless otherwise specified
Notional amounts of derivative open long positions	'
Derivative [Line Items]	'
Notional amounts of derivative open long positions	$3,137
Notional amounts of derivative open long positions | Foreign currency exchange contracts	'
Derivative [Line Items]	'
Notional amounts of derivative open long positions	2,805
Notional amounts of derivative open long positions | CFD contracts	'
Derivative [Line Items]	'
Notional amounts of derivative open long positions	331
Notional amounts of derivative open long positions | Metal contracts	'
Derivative [Line Items]	'
Notional amounts of derivative open long positions	1
Notional amounts of derivative open short positions	'
Derivative [Line Items]	'
Notional amounts of derivative open long positions	3,775
Notional amounts of derivative open short positions | Foreign currency exchange contracts	'
Derivative [Line Items]	'
Notional amounts of derivative open long positions	3,713
Notional amounts of derivative open short positions | CFD contracts	'
Derivative [Line Items]	'
Notional amounts of derivative open long positions	62
Notional amounts of derivative open short positions | Metal contracts	'
Derivative [Line Items]	'
Notional amounts of derivative open long positions	$0

ADDITIONAL_FINANCIAL_INFORMATI7

ADDITIONAL FINANCIAL INFORMATION - Net Gains Losses with Respect to Derivative Instruments (Detail) (USD $)	9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2013
Derivative [Line Items]	'
Net gains (losses) on derivative instruments, total	$143,708
Foreign currency exchange contracts	'
Derivative [Line Items]	'
Net gains (losses) on derivative instruments	88,111
CFD contracts	'
Derivative [Line Items]	'
Net gains (losses) on derivative instruments	11,324
Metal contracts	'
Derivative [Line Items]	'
Net gains (losses) on derivative instruments	$44,273

ADDITIONAL_FINANCIAL_INFORMATI8

ADDITIONAL FINANCIAL INFORMATION - Property and Equipment Including Leasehold Improvements and Capitalized Software Development Costs (Detail) (USD $)	Sep. 30, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified
Property, Plant and Equipment [Line Items]	'	'
Property and equipment	$41,739	$29,959
Less: Accumulated depreciation and amortization	-23,108	-18,936
Property and equipment, net	18,631	11,023
Software	'	'
Property, Plant and Equipment [Line Items]	'	'
Property and equipment	24,157	19,757
Computer equipment	'	'
Property, Plant and Equipment [Line Items]	'	'
Property and equipment	6,634	5,248
Leasehold improvements	'	'
Property, Plant and Equipment [Line Items]	'	'
Property and equipment	6,518	1,863
Telephone equipment	'	'
Property, Plant and Equipment [Line Items]	'	'
Property and equipment	725	725
Office equipment	'	'
Property, Plant and Equipment [Line Items]	'	'
Property and equipment	1,944	1,471
Furniture and fixtures	'	'
Property, Plant and Equipment [Line Items]	'	'
Property and equipment	1,107	241
Website development costs	'	'
Property, Plant and Equipment [Line Items]	'	'
Property and equipment	$654	$654

ADDITIONAL_FINANCIAL_INFORMATI9

ADDITIONAL FINANCIAL INFORMATION - Additional Information (Detail) (USD $)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2004	Dec. 31, 2003	Dec. 31, 2012
Accrued Liabilites [Line Items]	'	'	'	'	'	'	'
Other Accrued Liabilities, Current	$12,300,000	'	$12,300,000	'	'	'	'
Depreciation and amortization expense	1,852,000	1,126,000	5,234,000	3,234,000	'	'	'
Domain name acquired amount	'	'	'	'	100,000	300,000	'
Purchased intangible amortization	486,000	565,000	1,687,000	3,450,000	'	'	'
Goodwill	11,406,000	'	11,406,000	'	'	'	9,030,000
Increase in goodwill	'	'	$1,700,000	$1,000,000	'	'	'

Recovered_Sheet1

ADDITIONAL FINANCIAL INFORMATION - Definite-Lived Intangible Assets (Detail) (USD $)	Sep. 30, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified
Intangible Assets by Major Class [Line Items]	'	'
Cost	$49,584	$23,205
Accumulated Amortization	13,603	13,699
Customer lists	'	'
Intangible Assets by Major Class [Line Items]	'	'
Cost	21,974	19,356
Accumulated Amortization	13,237	12,138
Technology	'	'
Intangible Assets by Major Class [Line Items]	'	'
Cost	26,860	1,560
Accumulated Amortization	352	37
Trademark	'	'
Intangible Assets by Major Class [Line Items]	'	'
Cost	750	430
Accumulated Amortization	14	14
Non-compete agreement	'	'
Intangible Assets by Major Class [Line Items]	'	'
Cost	0	1,859
Accumulated Amortization	$0	$1,510

Recovered_Sheet2

ADDITIONAL FINANCIAL INFORMATION - Other Assets (Detail) (USD $)	Sep. 30, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified
Accounts, Notes, Loans and Financing Receivable [Line Items]	'	'
Receivables, Net, Current	$12,077	'
Vendor and security deposits	3,508	3,647
Current tax receivable	7,125	5,549
Deferred tax assets	3,338	4,968
Investment in Kapitall, Inc.	500	500
Miscellaneous receivables	8,422	2,489
Other assets, net	$34,970	$17,153

RELATED_PARTY_TRANSACTIONS_Add

RELATED PARTY TRANSACTIONS - Additional Information (Detail) (Management, USD $)	Sep. 30, 2013	Dec. 31, 2012
In Millions, unless otherwise specified
Management	'	'
Related Party Transaction [Line Items]	'	'
Payables to customers	$2.60	$2.40

ACQUISITION_Additional_Informa

ACQUISITION - Additional Information (Detail) (USD $)	3 Months Ended		9 Months Ended		3 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Dec. 31, 2012	Jun. 27, 2012
					GFT Income before tax [Member]	Open E Cry Limited Liability Company	Open E Cry Limited Liability Company
Business Acquisition [Line Items]	'	'	'	'	'	'	'
Business Combination, Pro Forma Information, Earnings or Loss of Acquiree since Acquisition Date, Actual	'	'	'	'	$700	'	'
Cash paid	'	'	'	'	'	2,700	12,000
INCOME BEFORE INCOME TAX EXPENSE	$8,643	$4,431	$38,216	$8,561	'	'	'

ACQUISITION_Schedule_of_Purcha

ACQUISITION - Schedule of Purchase Price (Detail) (USD $)	Sep. 30, 2013	Dec. 31, 2012	Jun. 27, 2012
In Thousands, unless otherwise specified		Open E Cry Limited Liability Company	Open E Cry Limited Liability Company
Business Acquisition [Line Items]	'	'	'
Business Acquisition, Contingent Consideration, Potential Cash Payment	$40,000	'	'
Cash paid	'	2,700	12,000
Working capital adjustment	'	'	2,691
Total purchase price	108,279	'	14,691
Loans Payable	33,200	'	'
Business Acquisition, Cost of Acquired Entity, Equity Interests Issued and Issuable	$35,079	'	'

ACQUISITION_Allocation_of_Purc

ACQUISITION - Allocation of Purchase Price to Fair Value of Assets and Liabilities (Detail) (USD $)

Sep. 30, 2013

Sep. 30, 2013

Jun. 27, 2012

Jun. 27, 2012

Jun. 27, 2012

Sep. 30, 2013

Sep. 30, 2013

Jun. 27, 2012

Jun. 27, 2012

Jun. 27, 2012

Jun. 27, 2012

Jun. 27, 2012

Jun. 27, 2012

Jun. 27, 2012

In Thousands, unless otherwise specified

Software GFT [Member]

Trademark

Technology

Customer Relationships

Customer List GFT [Member]

GFT Purchase Price Allocation, Goodwill [Member]

OEC Cash acquired [Member]

OEC Cust Cash Acquired [Member]

OEC Receivable from broker [Member]

OEC Other asssets [Member]

OEC Total assets [Member]

OEC Liabilities assumed [Member]

OEC Goodwill [Member]

Business Acquisition [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Cash and cash equivalents acquired

$15,781

'

'

'

'

'

'

$5,187

'

'

'

'

'

'

Cash and securities held for customers acquired

228,419

'

'

'

'

'

'

'

109,042

'

'

'

'

'

Business Acquisition, Purchase Price Allocation, Property, Plant and Equipment

7,515

'

'

'

'

'

'

'

'

'

'

'

'

'

Receivables from brokers acquired

61,028

'

'

'

'

'

'

'

'

815

'

'

'

'

Other assets acquired

18,928

'

'

'

'

'

'

'

'

'

98

'

'

'

Total tangible assets acquired

331,671

'

'

'

'

'

'

'

'

'

'

115,142

'

'

Total liabilities assumed

-253,558

'

'

'

'

'

'

'

'

'

'

'

-109,960

'

Identified intangible assets

'

'

650

1,630

630

'

'

'

'

'

'

'

'

'

Goodwill

'

'

'

'

'

'

1,715

'

'

'

'

'

'

6,599

Total purchase price

108,279

'

'

'

'

'

'

'

'

'

'

'

'

'

Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net

78,113

'

'

'

'

'

'

'

'

'

'

'

'

'

Business Acquisition, Net Consideration of Tangible Assets

30,165

'

'

'

'

'

'

'

'

'

'

'

'

'

Acquired Finite-lived Intangible Asset, Amount

$28,450

$25,300

'

'

'

$3,150

'

'

'

'

'

'

'

'

ACQUISITION_Acquisition_Cost_D

ACQUISITION Acquisition Cost (Details) (USD $)	3 Months Ended		9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Business Acquisition [Line Items]	'	'	'	'
Other Cost and Expense, Operating	$2,100	'	'	'
Business Combination, Acquisition Related Costs	451	85	1,456	85
OEC Acquisition related cost [Member]	'	'	'	'
Business Acquisition [Line Items]	'	'	'	'
Business Combination, Acquisition Related Costs	'	$100	'	'

ACQUISITION_Revenue_Details

ACQUISITION Revenue (Details) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2013
Segment Reporting, Revenue Reconciling Item [Line Items]	'
Other Cost and Expense, Operating	$2,100
GFT Expense [Member]	'
Segment Reporting, Revenue Reconciling Item [Line Items]	'
Revenue, Net	$2,800

ACQUISITION_Pro_Forma_Revenue_

ACQUISITION Pro Forma Revenue and Net Income (Details) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]	'	'	'	'
Non recurring expense	'	'	$8,800,000	'
Revenues, Excluding Interest and Dividends	60,571,000	39,908,000	183,157,000	118,938,000
Interest revenue	207,000	119,000	629,000	405,000
Interest Expense	180,000	42,000	428,000	428,000
Interest Income (Expense), Net	27,000	77,000	201,000	-23,000
Depreciation and amortization	1,852,000	1,126,000	5,234,000	3,234,000
Purchased intangible amortization	486,000	565,000	1,687,000	3,450,000
Business Combination, Acquisition Related Costs	451,000	85,000	1,456,000	85,000
Restructuring	439,000	0	439,000	634,000
Costs and Expenses	51,955,000	35,554,000	145,142,000	110,354,000
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Extraordinary Items, Noncontrolling Interest	8,643,000	4,431,000	38,216,000	8,561,000
Income tax expense	3,043,000	1,210,000	11,172,000	2,152,000
GFT Pro Forma Revenue before interest [Member]	'	'	'	'
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]	'	'	'	'
Revenues, Excluding Interest and Dividends	81,195,000	'	270,027,000	'
GFT/OEC Pro Forma Revenue before interest [Member] [Member]	'	'	'	'
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]	'	'	'	'
Revenues, Excluding Interest and Dividends	'	66,504,000	'	203,838,000
GFT Pro Forma Interest revenue [Member]	'	'	'	'
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]	'	'	'	'
Interest revenue	215,000	'	735,000	'
OEC Pro Forma Interest revenue [Member]	'	'	'	'
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]	'	'	'	'
Interest revenue	'	231,000	'	838,000
GFT Pro forma Interest expense [Member]	'	'	'	'
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]	'	'	'	'
Interest Expense	843,000	'	2,333,000	'
GFT/OEC Pro Forma Interest Expense [Member]	'	'	'	'
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]	'	'	'	'
Interest Expense	'	724,000	'	2,351,000
GFT Pro Forma Interest Income net [Member]	'	'	'	'
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]	'	'	'	'
Interest Income (Expense), Net	-628,000	'	-1,598,000	'
GFT/OEC Pro Forma Interest Income net [Member]	'	'	'	'
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]	'	'	'	'
Interest Income (Expense), Net	'	-493,000	'	-1,513,000
GFT Pro Forma Revenue, net [Member]	'	'	'	'
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]	'	'	'	'
Revenue, Net	80,567,000	'	268,429,000	'
GFT/OEC Pro Forma Revenue, net [Member]	'	'	'	'
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]	'	'	'	'
Revenue, Net	'	66,011,000	'	202,325,000
GFT Pro Forma Depreciation Amortization [Member]	'	'	'	'
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]	'	'	'	'
Depreciation and amortization	2,519,000	'	7,536,000	'
GFT/OEC Pro Forma Depreciation Amortization [Member]	'	'	'	'
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]	'	'	'	'
Depreciation and amortization	'	2,100,000	'	6,082,000
GFT Pro Forma Amortization [Member]	'	'	'	'
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]	'	'	'	'
Purchased intangible amortization	1,215,000	'	3,997,000	'
OEC Pro Forma Amortization [Member]	'	'	'	'
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]	'	'	'	'
Purchased intangible amortization	'	1,444,000	'	6,057,000
GFT Pro Forma Acquisistion expense [Member]	'	'	'	'
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]	'	'	'	'
Business Combination, Acquisition Related Costs	451,000	'	1,456,000	'
GFT/OEC Pro Forma Acquisistion expense [Member] [Member]	'	'	'	'
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]	'	'	'	'
Business Combination, Acquisition Related Costs	'	85,000	'	85,000
GFT Pro Forma Restructuring Expense [Member]	'	'	'	'
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]	'	'	'	'
Restructuring	439,000	'	439,000	'
GFT/OEC Pro Forma Restructuring Expense [Member]	'	'	'	'
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]	'	'	'	'
Restructuring	'	'	'	634,000
GFT Pro Forma Other Expense [Member]	'	'	'	'
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]	'	'	'	'
Other Expenses	70,902,000	'	230,221,000	'
GFT/OEC Pro Forma Other Expense [Member] [Member]	'	'	'	'
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]	'	'	'	'
Other Expenses	'	64,435,000	'	200,559,000
GFT Pro Forma Total Expense [Member]	'	'	'	'
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]	'	'	'	'
Costs and Expenses	75,526,000	'	243,649,000	'
GFT/OEC Pro Forma Total Expense [Member] [Member]	'	'	'	'
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]	'	'	'	'
Costs and Expenses	'	68,064,000	'	213,417,000
GFT Pro Forma Income before tax [Member]	'	'	'	'
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]	'	'	'	'
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Extraordinary Items, Noncontrolling Interest	5,041,000	'	24,780,000	'
GFT/OEC Pro Forma Income before tax [Member] [Member]	'	'	'	'
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]	'	'	'	'
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Extraordinary Items, Noncontrolling Interest	'	-2,053,000	'	-11,092,000
GFT Pro Forma Income Tax expense [Member]	'	'	'	'
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]	'	'	'	'
Income tax expense	1,890,000	'	9,293,000	'
GFT/OEC Pro Forma Income Tax expense [Member] [Member]	'	'	'	'
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]	'	'	'	'
Income tax expense	'	-770,000	'	-4,159,000
GFT Pro Forma Net Income/(Loss) [Member]	'	'	'	'
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]	'	'	'	'
Business Acquisition, Pro Forma Net Income (Loss)	3,151,000	'	15,487,000	'
GFT/OEC Pro Forma Net Income/(Loss) [Member] [Member]	'	'	'	'
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]	'	'	'	'
Business Acquisition, Pro Forma Net Income (Loss)	'	($1,283,000)	'	($6,933,000)

TERM_LOAN_AND_REVOLVER_Additio

TERM LOAN AND REVOLVER - Additional Information (Detail) (USD $)	9 Months Ended
	Sep. 30, 2013
Debt Instrument [Line Items]	'
Debt Instrument, Interest Rate, Stated Percentage	8.00%
Debt Instrument, Periodic Payment, Principal	$1,500,000

SHARE_BASED_COMPENSATION_Addit

SHARE BASED COMPENSATION - Additional Information (Detail) (Employees And Non Employee Directors, USD $)	9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012
Employees And Non Employee Directors	'	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'
Restricted stock, shares granted	0.8	0.6
Stock options, shares granted	0.5	0.3
Restricted stock, values granted	$3.60	$3.10
Stock options, values granted	$0.60	$0.70

SHARE_BASED_COMPENSATION_Assum

SHARE BASED COMPENSATION - Assumptions for Stock Options Granted (Detail)	9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012
Valuation Assumptions	'	'
Risk-free rate	0.80%	0.90%
Expected volatility	48.80%	48.50%
Expected term (years)	'4 years 9 months	'4 years 9 months
Dividend yield	4.90%	0.00%

EARNINGS_PER_COMMON_SHARE_Addi

EARNINGS PER COMMON SHARE - Additional Information (Detail)	3 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012
Earnings Per Share [Abstract]	'	'
Anti-dilutive stock options excluded from calculation of diluted earnings per share	0.6	0.3

EARNINGS_PER_COMMON_SHARE_Comp

EARNINGS PER COMMON SHARE - Computation of Earnings Per Share (Detail) (USD $)	3 Months Ended				9 Months Ended
In Thousands, except Share data, unless otherwise specified	Sep. 30, 2013		Sep. 30, 2012		Sep. 30, 2013		Sep. 30, 2012
Earnings Per Share [Abstract]	'		'		'		'
Net income	$5,600		$3,221		$27,044		$6,409
Adjustment	0	[1]	0	[1]	154	[1]	0	[1]
Net income applicable to GAIN common shareholders	$5,600		$3,221		$26,890		$6,409
Weighted average common shares outstanding:	'		'		'		'
Basic weighted average common shares outstanding	36,062,659		35,250,404		35,563,701		34,893,622
Effect of dilutive securities:	'		'		'		'
Stock options (in shares)	1,620,851		1,382,802		1,244,009		1,764,568
RSUs/RSAs (in shares)	2,047,347		1,927,451		1,914,957		2,269,483
Diluted weighted average common shares outstanding	39,730,857		38,560,657		38,722,667		38,927,673
Earnings per common share	'		'		'		'
Basic (usd per share)	$0.16		$0.09		$0.76		$0.18
Diluted (usd per share)	$0.14		$0.08		$0.69		$0.16
[1]	During the period an adjustment to retained earnings was made, reflecting the amounts deemed uncollectible associated with previously issued preferred stock, which was converted to common stock immediately prior to the IPO.

LEGAL_Additional_Information_D

LEGAL - Additional Information (Detail)	Sep. 30, 2013
	cases
Long-term Purchase Commitment [Line Items]	'
Number of alleged patent infringement lawsuit against the company	11
Open E Cry Limited Liability Company	'
Long-term Purchase Commitment [Line Items]	'
Number of alleged patent infringement lawsuit against the company	12

INCOME_TAXES_Additional_Inform

INCOME TAXES - Additional Information (Detail) (USD $)	3 Months Ended		9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Income Tax Disclosure [Abstract]	'	'	'	'
Provision for income taxes expense (benefit)	$3,043	$1,210	$11,172	$2,152
Effective income tax rates	35.20%	27.30%	29.20%	25.10%

REGULATORY_REQUIREMENTS_Minimu

REGULATORY REQUIREMENTS - Minimum Regulatory Capital Subsidiaries Required to Maintain (Detail) (USD $)	Sep. 30, 2013
In Millions, unless otherwise specified
Schedule Of Compliance With Regulatory Capital Requirements For Broker Dealer [Line Items]	'
Minimum Regulatory Capital Requirements	$94.90
Capital Levels Maintained	169.6
Excess Net Capital	74.7
Percent of Requirement Maintained	179.00%
GAIN Capital Group, LLC	'
Schedule Of Compliance With Regulatory Capital Requirements For Broker Dealer [Line Items]	'
Minimum Regulatory Capital Requirements	24.8
Capital Levels Maintained	44.1
Excess Net Capital	19.3
Percent of Requirement Maintained	178.00%
GAIN Capital Securities, Inc.	'
Schedule Of Compliance With Regulatory Capital Requirements For Broker Dealer [Line Items]	'
Minimum Regulatory Capital Requirements	0.1
Capital Levels Maintained	0.2
Excess Net Capital	0.1
Percent of Requirement Maintained	200.00%
GAIN Capital-Forex.com U.K., Ltd.	'
Schedule Of Compliance With Regulatory Capital Requirements For Broker Dealer [Line Items]	'
Minimum Regulatory Capital Requirements	20.9
Capital Levels Maintained	50.5
Excess Net Capital	29.6
Percent of Requirement Maintained	242.00%
Forex.com Japan Co., Ltd.	'
Schedule Of Compliance With Regulatory Capital Requirements For Broker Dealer [Line Items]	'
Minimum Regulatory Capital Requirements	3.5
Capital Levels Maintained	10.8
Excess Net Capital	7.3
Percent of Requirement Maintained	309.00%
GAIN Capital Forex.com Australia, Pty. Ltd.	'
Schedule Of Compliance With Regulatory Capital Requirements For Broker Dealer [Line Items]	'
Minimum Regulatory Capital Requirements	0.4
Capital Levels Maintained	2.7
Excess Net Capital	2.3
Percent of Requirement Maintained	675.00%
GAIN Capital-Forex.com Hong Kong, Ltd.	'
Schedule Of Compliance With Regulatory Capital Requirements For Broker Dealer [Line Items]	'
Minimum Regulatory Capital Requirements	1.9
Capital Levels Maintained	3.8
Excess Net Capital	1.9
Percent of Requirement Maintained	200.00%
GAIN Global Markets, Inc.	'
Schedule Of Compliance With Regulatory Capital Requirements For Broker Dealer [Line Items]	'
Minimum Regulatory Capital Requirements	0.1
Capital Levels Maintained	0.3
Excess Net Capital	0.2
Percent of Requirement Maintained	300.00%
GAIN Capital-Forex.com Canada Ltd.	'
Schedule Of Compliance With Regulatory Capital Requirements For Broker Dealer [Line Items]	'
Minimum Regulatory Capital Requirements	0.2
Capital Levels Maintained	1.9
Excess Net Capital	1.7
Percent of Requirement Maintained	950.00%
Global Futures & Forex Ltd [Member]	'
Schedule Of Compliance With Regulatory Capital Requirements For Broker Dealer [Line Items]	'
Minimum Regulatory Capital Requirements	1
Global Futures & Forex Ltd. [Member]	'
Schedule Of Compliance With Regulatory Capital Requirements For Broker Dealer [Line Items]	'
Capital Levels Maintained	1.6
Global Futures & Forex Lt [Member]	'
Schedule Of Compliance With Regulatory Capital Requirements For Broker Dealer [Line Items]	'
Excess Net Capital	0.6
Global Futures & Forex [Member]	'
Schedule Of Compliance With Regulatory Capital Requirements For Broker Dealer [Line Items]	'
Percent of Requirement Maintained	160.00%
GFT Global Forex UK Ltd [Member]	'
Schedule Of Compliance With Regulatory Capital Requirements For Broker Dealer [Line Items]	'
Minimum Regulatory Capital Requirements	40.4
GFT Global Market UK Ltd. [Member]	'
Schedule Of Compliance With Regulatory Capital Requirements For Broker Dealer [Line Items]	'
Capital Levels Maintained	51.9
GFT Global Markets UK Ltd [Member]	'
Schedule Of Compliance With Regulatory Capital Requirements For Broker Dealer [Line Items]	'
Excess Net Capital	11.5
GFT Global Markets UK [Member]	'
Schedule Of Compliance With Regulatory Capital Requirements For Broker Dealer [Line Items]	'
Percent of Requirement Maintained	128.00%
GFT Global Markets Asia Pte. Ltd [Member]	'
Schedule Of Compliance With Regulatory Capital Requirements For Broker Dealer [Line Items]	'
Minimum Regulatory Capital Requirements	1.6
GFT Global Markets Asia Pte Ltd [Member]	'
Schedule Of Compliance With Regulatory Capital Requirements For Broker Dealer [Line Items]	'
Capital Levels Maintained	1.8
GFT Global Markets Asia Pte [Member]	'
Schedule Of Compliance With Regulatory Capital Requirements For Broker Dealer [Line Items]	'
Excess Net Capital	$0.20
GFT Global Markets Asia [Member]	'
Schedule Of Compliance With Regulatory Capital Requirements For Broker Dealer [Line Items]	'
Percent of Requirement Maintained	113.00%

REGULATORY_REQUIREMENTS_Additi

REGULATORY REQUIREMENTS - Additional Information (Detail) (GAIN Capital Forex.com Australia, Pty. Ltd.)	Sep. 30, 2013	Sep. 30, 2013
In Millions, unless otherwise specified	USD ($)	AUD
Schedule Of Compliance With Regulatory Capital Requirements For Broker Dealer [Line Items]	'	'
Net capital requirement	$0.50	0.5
Minimum capital requirement as percentage of average revenue	5.00%	5.00%

SEGMENT_INFORMATION_Additional

SEGMENT INFORMATION - Additional Information (Detail)	9 Months Ended
	Sep. 30, 2013
	Segment
Segment Reporting Information [Line Items]	'
Number of operating segments	1
Maximum	'
Segment Reporting Information [Line Items]	'
Percentage of revenue from a single customer	10.00%

SUBSEQUENT_EVENTS_Additional_I

SUBSEQUENT EVENTS - Additional Information (Detail) (USD $)	9 Months Ended	0 Months Ended	1 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Sep. 30, 2013	Aug. 08, 2013	Oct. 31, 2013
		Quarterly dividend declared	Quarterly dividend declared
Subsequent Event [Line Items]	'	'	'
Common stock dividend declared per share	'	$0.05	'
Common stock dividend declared, payable date	'	'	20-Dec-13
Common stock dividend declared, record date	'	'	12-Dec-13
Repurchase of shares, value	$987	'	'