GAIN Capital 10-Q 6 Nov 18 2018 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2018	Oct. 26, 2018
Document Documentand Entity Information [Abstract]
Entity Registrant Name	GAIN Capital Holdings, Inc.
Trading Symbol	GCAP
Entity Central Index Key	1,444,363
Current Fiscal Year End Date	--12-31
Entity Filer Category	Accelerated Filer
Entity Emerging Growth Company	false
Entity Small Business	false
Document Type	10-Q
Document Period End Date	Sep. 30, 2018
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	Q3
Amendment Flag	false
Entity Common Stock, Shares Outstanding		44,281,501

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
ASSETS:
Cash and cash equivalents	$ 362,345	$ 209,688
Cash and cash equivalents held for customers	887,282	978,828
Receivables from brokers	57,452	78,503
Property and equipment, net	33,457	40,742
Intangible assets, net	36,195	61,969
Goodwill	28,044	33,036
Other assets	37,489	45,881
Total assets	1,442,264	1,448,647
Liabilities
Payables to customers	887,282	978,828
Payables to brokers	1,754	2,789
Accrued compensation and benefits	11,118	10,104
Accrued expenses and other liabilities	38,031	33,947
Income tax payable	7,461	599
Convertible senior notes	136,864	132,221
Total liabilities	1,082,510	1,158,488
Commitments and contingent liabilities
Redeemable non-controlling interests	2,543	4,411
Shareholders’ equity
Common stock ($0.00001 par value; 120 million shares authorized, 54,355,426 shares issued and 44,335,477 shares outstanding as of September 30, 2018; 120 million shares authorized, 53,612,340 shares issued and 45,152,299 shares outstanding as of December 31, 2017)	0	0
Additional paid-in capital	241,124	235,659
Retained earnings	209,157	122,686
Accumulated other comprehensive loss	(24,538)	(15,670)
Treasury stock, at cost (10,019,949 shares at September 30, 2018 and 8,460,041 at December 31, 2017)	(68,532)	(56,927)
Total shareholders’ equity	357,211	285,748
Total liabilities and shareholders’ equity	$ 1,442,264	$ 1,448,647

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Sep. 30, 2018	Dec. 31, 2017
Statement of Financial Position [Abstract]
Common stock, par value (in dollars per share)	$ 0.00001	$ 0.00001
Common stock, shares authorized (in shares)	120,000,000	120,000,000
Common stock, shares issued (in shares)	54,355,426	53,612,340
Common stock, shares outstanding (in shares)	44,335,477	45,152,299
Treasury stock, shares (in shares)	10,019,949	8,460,041

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations and Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
REVENUE:
Total non-interest revenue	$ 92,754	$ 72,403	$ 271,164	$ 212,391
Interest revenue	3,305	1,621	8,206	3,703
Interest expense	518	264	1,284	563
Total net interest revenue	2,787	1,357	6,922	3,140
Net revenue	95,541	73,760	278,086	215,531
EXPENSES:
Employee compensation and benefits	22,853	20,811	69,664	64,345
Selling and marketing	10,215	6,402	22,953	23,154
Referral fees	8,148	12,924	30,043	42,677
Trading expenses	5,770	4,741	17,122	15,075
General and administrative	12,207	11,221	38,899	32,285
Depreciation and amortization	4,685	4,373	15,394	12,322
Purchased intangible amortization	3,504	3,524	10,784	10,407
Communications and technology	5,507	4,635	16,393	14,161
Bad debt provision	334	143	1,734	49
Restructuring expenses	0	0	25	0
Contingent provision	4,975	0	4,975	0
Impairment of investment	0	0	(130)	0
Total operating expense	78,198	68,774	227,856	214,475
OPERATING PROFIT	17,343	4,986	50,230	1,056
Interest expense on long term borrowings	3,404	2,985	10,132	8,344
Loss on extinguishment of debt	0	4,944	0	4,944
INCOME/(LOSS) BEFORE INCOME TAX EXPENSE/(BENEFIT)	13,939	(2,943)	40,098	(12,232)
Income tax (benefit)/expense	3,970	97	11,383	(4,300)
Equity in net loss of affiliate	0	(40)	0	(94)
Net income/(loss) from continuing operations	9,969	(3,080)	28,715	(8,026)
Income from discontinued operations, including gain on sale of $69,439, net of income tax of $3,222	2,344	725	67,330	977
NET INCOME/(LOSS)	12,313	(2,355)	96,045	(7,049)
Less income attributable to non-controlling interest	137	225	638	463
NET INCOME/(LOSS) APPLICABLE TO GAIN CAPITAL HOLDINGS, INC.	12,176	(2,580)	95,407	(7,512)
Other comprehensive income:
Foreign currency translation adjustment	(3,185)	6,758	(8,868)	19,059
COMPREHENSIVE INCOME APPLICABLE TO GAIN CAPITAL HOLDINGS, INC.	8,991	4,178	86,539	11,547
Retail revenue
REVENUE:
Revenue from contract with customer	82,917	62,143	239,069	180,153
Futures revenue
REVENUE:
Revenue from contract with customer	8,666	9,031	30,440	29,176
Other revenue
REVENUE:
Revenue from contract with customer	$ 1,171	$ 1,229	$ 1,655	$ 3,062

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Operations and Comprehensive Income (Parenthetical) $ in Thousands	3 Months Ended
	Jun. 30, 2018USD ($)
Income Statement [Abstract]
Gain on sale	$ 69,439
Income tax	$ 3,222

Condensed Consolidated Statem_3

Condensed Consolidated Statement of Changes in Shareholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Treasury Stock	Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Loss
BEGINNING BALANCE (in shares) at Dec. 31, 2016		48,220,243
BEGINNING BALANCE at Dec. 31, 2016	$ 294,182	$ 0	$ (30,767)	$ 218,392	$ 143,399	$ (36,842)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss) applicable to Gain Capital Holdings, Inc.	(7,512)				(7,512)
Exercise of options (in shares)		82,774
Exercise of options	335			335
Conversion of restricted stock into common stock (in shares)		526,113
Issuance of common stock for the employee stock purchase plan (in shares)		64,546
Issuance of common stock for the employee stock purchase plan	402			402
Purchase of treasury stock (in shares)		(3,776,283)
Purchase of treasury stock	(25,778)		(25,778)
Shares withheld for net settlements of share-based awards (in shares)		(55,190)
Shares withheld for net settlements of share-based awards	(382)		(382)
Share-based compensation	3,855			3,855
Recognition of debt discount on convertible notes	18,399			18,399
Tax effect of debt discount on convertible notes	(7,024)			(7,024)
Repurchase of convertible notes	(186)			(186)
Adjustment to fair value of redeemable non-controlling interests	1,711				1,711
Dividends declared ($0.06 per share)	(8,469)				(8,469)
Foreign currency translation adjustment	19,059					19,059
ENDING BALANCE (in shares) at Sep. 30, 2017		45,062,203
ENDING BALANCE at Sep. 30, 2017	288,592	$ 0	(56,927)	234,173	129,129	(17,783)
BEGINNING BALANCE (in shares) at Dec. 31, 2017		45,152,299
BEGINNING BALANCE at Dec. 31, 2017	285,748	$ 0	(56,927)	235,659	122,686	(15,670)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss) applicable to Gain Capital Holdings, Inc.	95,407				95,407
Exercise of options (in shares)		87,000
Exercise of options	597			597
Conversion of restricted stock into common stock (in shares)		614,551
Conversion of restricted stock into common stock	0
Issuance of common stock for the employee stock purchase plan (in shares)		41,535
Issuance of common stock for the employee stock purchase plan	314			314
Purchase of treasury stock (in shares)		(1,550,504)
Purchase of treasury stock	(11,530)		(11,530)
Shares withheld for net settlements of share-based awards (in shares)		(9,404)
Shares withheld for net settlements of share-based awards	(75)		(75)
Share-based compensation	4,554			4,554
Adjustment to fair value of redeemable non-controlling interests	(901)				(901)
Dividends declared ($0.06 per share)	(8,035)				(8,035)
Foreign currency translation adjustment	(8,868)					(8,868)
ENDING BALANCE (in shares) at Sep. 30, 2018		44,335,477
ENDING BALANCE at Sep. 30, 2018	$ 357,211	$ 0	$ (68,532)	$ 241,124	$ 209,157	$ (24,538)

Condensed Consolidated Statem_4

Condensed Consolidated Statement of Changes in Shareholders' Equity (Parenthetical) - $ / shares	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Statement of Stockholders' Equity [Abstract]
Dividends declared (usd per share)	$ 0.06	$ 0.06

Condensed Consolidated Statem_5

Condensed Consolidated Statement of Cash Flows - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income/(loss)	$ 12,313	$ (2,355)	$ 96,045	$ (7,049)
Adjustments to reconcile net income/(loss) to cash (used in)/provided by operating activities
Loss/(gain) on foreign currency exchange rates			1,092	(234)
Depreciation and amortization			27,460	24,974
Deferred tax benefit			(2,009)	(7,025)
Amortization of deferred financing costs			489	332
Bad debt provision	334	143	1,734	49
Convertible senior notes discount amortization			4,153	3,438
Share-based compensation			4,554	3,855
Loss on extinguishment of debt			0	(4,944)
Equity in net loss of affiliate	0	40	0	94
Gain on sale of GTX			(69,439)	0
Changes in operating assets and liabilities:
Receivables from brokers			20,833	2,488
Other assets			4,937	1,490
Payables to customers			(103,889)	(18,532)
Payables to brokers			(877)	0
Accrued compensation and benefits			(1,688)	(3,343)
Accrued expenses and other liabilities			3,366	(9,882)
Income tax payable			8,131	5,753
Net cash provided by/(used in) operating activities			(5,108)	1,352
Cash provided by/(used in) operating activities - continuing operations			(23,802)	16,060
Cash provided by/(used in) operating activities - discontinued operations			18,694	(14,708)
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchases of property and equipment			(11,494)	(16,698)
Purchase of minority interest in GAA			(2,854)	0
Proceeds from sale of GTX			96,518	0
Acquisition of FXCM assets			0	(7,184)
Net cash provided by/(used in) investing activities			82,170	(23,882)
Cash used in investing activities - continuing operations			(13,504)	(22,904)
Cash provided by/(used in) investing activities - discontinued operations			95,674	(978)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from exercise of stock options			597	335
Proceeds from employee stock purchase plan			314	402
Purchase of treasury stock			(11,605)	(26,160)
Dividend payments			(8,035)	(8,468)
Distributions to non-controlling interest holders			(553)	(983)
Convertible note issuance, net			0	89,010
Repurchase of convertible notes			0	(73,057)
Net cash used in financing activities			(19,282)	(18,921)
Effect of exchange rate changes on cash and cash equivalents			3,331	46,421
NET INCREASE IN CASH, CASH EQUIVALENTS, AND RESTRICTED CASH			61,111	4,970
CASH, CASH EQUIVALENTS, AND RESTRICTED CASH — Beginning of period			1,188,516	1,180,228	$ 1,180,228
CASH, CASH EQUIVALENTS, AND RESTRICTED CASH — End of period	1,249,627	1,185,198	1,249,627	1,185,198	1,188,516
Cash and cash equivalents						$ 362,345	$ 209,688	$ 225,581
Cash and cash equivalents held for customers						887,282		959,617
CASH, CASH EQUIVALENTS, AND RESTRICTED CASH — End of period	1,249,627	1,185,198	1,188,516	1,180,228	$ 1,180,228	$ 1,249,627	$ 1,188,516	$ 1,185,198
Cash paid during the year for:
Interest			(8,401)	(3,412)
Income taxes			(7,406)	(4,701)
Non-cash financing activities:
Adjustment to the redemption value of non-controlling interests	$ (10)	$ 728	$ (901)	$ 1,711

DESCRIPTION OF BUSINESS AND BAS

DESCRIPTION OF BUSINESS AND BASIS OF PRESENTATION	9 Months Ended
	Sep. 30, 2018
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 of GAIN Capital Group, LLC (“Group, LLC”), the Company’s primary regulated entity in the United States. GAIN Capital Holdings Ltd. is the holding company of the Company’s primary regulated entity in the United Kingdom. The Company is a global provider of trading services and solutions, specializing in over-the-counter, or OTC, and exchange-traded markets. The Company operates its business in two segments. Through its retail segment, the Company provides its retail customers around the world with access to a diverse range of global financial markets, including spot forex, precious metals, as well as spread bets and contracts for difference, or CFDs, on currencies, commodities, indices, individual equities, cryptocurrencies, bonds and interest rate products, as well as OTC options. The Company’s futures segment offers execution and risk management services for exchange-traded products on major U.S. and European exchanges, including Bitcoin. For more information about the Company’s segments, please see Note 19 . Group, LLC is a retail foreign exchange dealer (“RFED”) and a Futures Commission Merchant (“FCM”) registered with the Commodity Futures Trading Commission (the “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. GAIN Capital UK Limited (“GCUK”) is registered in the United Kingdom (“U.K.”) and regulated by the Financial Conduct Authority (“FCA”) as a full scope €730k IFPRU Investment Firm. Sale of GTX ECN Business On June 29, 2018, the Company completed the sale of the GTX ECN business, which previously comprised the Company's institutional segment, to Deutsche Börse Group via its FX unit, 360T, for a total purchase price of $100 million less a working capital adjustment which amounted to a $0.2 million reduction in the purchase price. The Company determined that the institutional segment met the discontinued operations criteria set forth in Accounting Standards Codification (ASC) Subtopic 205-20-45, Presentation of Financial Statements , in the quarter ended June 30, 2018. As such, the institutional segment results have been classified as discontinued operations in the accompanying Condensed Consolidated Statements of Operations and Comprehensive Income. For more information relating to the discontinued operations of the Company's GTX ECN business, please see Note 3 . Basis of Presentation and Principles of Consolidation The accompanying unaudited Condensed Consolidated Financial Statements reflect all adjustments that, in the opinion of management, are necessary for a fair presentation of the financial statements for the interim periods. The financial statements are presented in accordance with accounting principles generally accepted in the United States of America (“U.S. GAAP”). The unaudited Condensed Consolidated Financial Statements have been prepared in accordance with the Securities and Exchange Commission's (“SEC”) regulations 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 audited Consolidated Financial Statements and related notes included in the Company’s Annual Report on Form 10-K as of and for the year ended December 31, 2017 . The unaudited Condensed Consolidated Financial Statements include the accounts of the Company and its wholly-owned subsidiaries, after the elimination of inter-company transactions and balances.

ACCOUNTING PRONOUNCEMENTS

ACCOUNTING PRONOUNCEMENTS	9 Months Ended
	Sep. 30, 2018
Accounting Changes and Error Corrections [Abstract]
ACCOUNTING PRONOUNCEMENTS	ACCOUNTING PRONOUNCEMENTS Recently Adopted In January 2017, the Financial Accounting Standards Board (the “FASB”) issued ASU No. 2017-04, “Intangibles-Goodwill and Other (Topic 350): Simplifying the Test for Goodwill Impairment,” which eliminates the requirement to calculate the implied fair value of goodwill to measure a goodwill impairment charge (Step 2) from the goodwill impairment test. Instead, an impairment charge will equal the amount by which a reporting unit’s carrying amount exceeds its fair value, not to exceed the amount of goodwill allocated to the reporting unit. The guidance will be effective for the Company for its annual or any interim goodwill impairment tests in fiscal years beginning after December 15, 2019, with early adoption permitted after January 1, 2017 . The Company has adopted this ASU as of January 1, 2018, and will apply Step 2 going forward to the extent it is required. In November 2016, the FASB issued ASU No. 2016-18, “Restricted Cash,” which requires that companies present cash, cash equivalents and amounts generally described as restricted cash or restricted cash equivalents (restricted cash) when reconciling beginning-of-period and end-of-period totals on the Statement of Cash Flows. The Company has retrospectively adopted this ASU as of January 1, 2018 and includes cash and cash equivalents held for customers as restricted cash. As a result, Net cash provided by operating activities on the Statement of Cash Flows decreased by $18.5 million for the nine months ended September 30, 2017. The Company defines restricted cash to include cash and cash equivalents held for customers, which represents cash and other highly liquid assets held to fund customer liabilities in connection with trading positions. Included in this balance are funds deposited by customers and funds accruing to customers as a result of trades or contracts. The Company records a corresponding liability in connection with this amount in Payables to customers. In addition, the Company holds certain customer funds in segregated or secured broker accounts. Legally segregated balances are not available for general use, in accordance with certain jurisdictional regulatory requirements. In May 2014, the FASB issued ASU No. 2014-09, “Revenue from Contracts with Customers”, which is part of ASC Topic 606. It defines how companies report revenues from contracts with customers and also requires certain enhanced disclosures. The standard’s provisions and related amendments are effective for annual reporting periods beginning after December 15, 2017. On January 1, 2018, the Company adopted this guidance, which did not have a material impact on the Company’s financial statements. A substantial portion of revenue falls under ASC Topic 825, Financial Instruments, which is excluded from the scope of the new guidance. The Company adopted ASU No. 2014-09 using the modified retrospective approach. See Note 4 Revenue Recognition for additional disclosure. Not Yet Adopted In February 2016, the FASB issued ASU No. 2016-02, “Leases (Topic 842),” which amended the guidance on accounting for leases. The FASB issued this update to increase transparency and comparability among organizations. This update requires recognizing lease assets and lease liabilities on the balance sheet and disclosing key information about leasing arrangements. The guidance is effective for fiscal years beginning after December 15, 2018 , including interim periods within that fiscal year. We are in the process of collecting and reviewing leases that have been entered into by the Company within the scope of ASC 842, including potential disclosures, in order to complete our evaluation of the impact of the standard on our consolidated financial statements prior to the end of 2018. In addition, we continue to monitor additional changes, modifications, clarifications or interpretations undertaken by the FASB or others, which may impact our current conclusions. We will adopt the requirements of the new standard effective January 1, 2019. In February 2018, the FASB issued ASU No. 2018-02, “Income Statement - Reporting Comprehensive Income (Topic 220),” to address certain income tax effects in Accumulated Other Comprehensive Income (AOCI) resulting from the tax reform enacted in 2017. The amended guidance provides an option to reclassify tax effects within AOCI to retained earnings in the period in which the effect of the tax reform is recorded. The amendments are effective for fiscal years beginning after December 15, 2018 , including interim periods. Early adoption is permitted. This will not have an impact on the Company as there are no balances in AOCI that are tax effected.

DISCONTINUED OPERATIONS

DISCONTINUED OPERATIONS	9 Months Ended
	Sep. 30, 2018
Discontinued Operations and Disposal Groups [Abstract]
DISCONTINUED OPERATIONS	DISCONTINUED OPERATIONS On June 29, 2018, the Company completed the sale of its GTX ECN business, which previously comprised the Company's institutional segment, to Deutsche Börse via its FX unit, 360T, for a total purchase price of $100 million less a working capital adjustment which amounted to a $0.2 million reduction in purchase price. The Company recorded a gain of $69.4 million on the sale of the GTX business. The Company determined that the sale of the GTX business qualifies as a discontinued operation under the criteria set forth in Accounting Standards Codification 205-20-45, Presentation of Financial Statements and the Company does not have any significant continuing involvement in these operations. The results of operations from the discontinued segment for the three and nine months ended September 30, 2018 are as follows (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2018 2017 2018 2017 REVENUE: Institutional revenue $ — $ 7,520 $ 16,379 $ 23,322 Other revenue/(loss) — — (2 ) — Total non-interest revenue — 7,520 16,377 23,322 Interest revenue — 33 103 81 Total net interest revenue — 33 103 81 Net revenue $ — $ 7,553 $ 16,480 $ 23,403 EXPENSES: Employee compensation and benefits $ 94 $ 2,993 $ 5,973 $ 9,999 Trading expenses — 2,409 5,439 7,320 Other expenses 30 1,104 3,955 4,287 Total operating expense 124 6,506 15,367 21,606 OPERATING PROFIT/(LOSS) (124 ) 1,047 1,113 1,797 Gain/(loss) on sale of discontinued operations (142 ) — 69,439 — INCOME/(LOSS) BEFORE INCOME TAX EXPENSE/(BENEFIT) (266 ) 1,047 70,552 1,797 Income tax expense/(benefit) (2,610 ) 322 3,222 820 NET INCOME FROM DISCONTINUED OPERATIONS $ 2,344 $ 725 $ 67,330 $ 977 Since the sale of the GTX ECN business closed on June 29, 2018, there were no assets held for sale as of September 30, 2018. As of December 31, 2017, total assets of $28.5 million and total liabilities of $3.8 million were related to the discontinued segment.

REVENUE RECOGNITION

REVENUE RECOGNITION	9 Months Ended
	Sep. 30, 2018
Revenue from Contract with Customer [Abstract]
REVENUE RECOGNITION	REVENUE RECOGNITION In May 2014, the FASB issued ASU No. 2014-09, “Revenue from Contracts with Customers”, which is part of ASC Topic 606. It defines how companies report revenues from contracts with customers and also requires certain enhanced disclosures. The standard’s provisions and related amendments are effective for annual reporting periods beginning after December 15, 2017. On January 1, 2018, the Company adopted this guidance, which did not have a material impact on the Company’s financial statements. A substantial portion of the Company's retail revenue as well as interest revenue falls under ASC Topic 825, “Financial Instruments”, which is excluded from the scope of Topic 606. Additionally, the Company’s futures segment revenue was not materially impacted as the satisfaction of performance obligations under the new guidance is materially consistent with the Company’s previous revenue recognition policies. Accordingly, the adoption of the new standard did not result in a transition adjustment to opening retained earnings, and as a result, revenues for contracts with customers would not have been adjusted in prior periods and are not presented herein on an adjusted basis. Similarly, the amended guidance did not have a material impact on the recognition of costs incurred to obtain new contracts. As a result of the adoption of the new guidance, the Company recorded a gross up of $1.0 million for the nine months ended September 30, 2018 which impacted referral fee expense in the Company's discontinued operations. There was no gross up required for the three months ended September 30, 2018 . The Company adopted ASU No. 2014-09 using the modified retrospective approach. Under ASC Topic 606, revenues are recognized when control of the promised goods or services is transferred to customers in exchange for an amount that reflects the consideration the Company expects to be entitled to in transferring those goods or services. The following is a description of the Company’s revenue recognition policies as they relate to revenue from contracts with customers. Futures Revenue Futures revenue consists primarily of commissions earned on futures and futures options trades. The Company acts as an agent for the trades executed in our futures segment and are not exposed to market risk in connection with that activity. The Company earns commission revenue by acting as an agent on behalf of customers. The Company’s futures revenue performance obligations also consist of trade execution and are satisfied on the trade date; accordingly, commission revenues are recorded on the trade date. Disaggregation of Revenues The following table presents the Company’s revenue from contracts with customers disaggregated by the services described above for the futures segment for the three and nine months ended September 30, 2018 : Three months ended September 30, 2018 Nine months ended September 30, 2018 Futures Direct Customers (1) $ 2,106 $ 7,272 Indirect Customers (2) 5,270 18,854 Other 2,361 7,202 Total Segment Revenue $ 9,737 $ 33,328 (1) Direct customers are all customers not classified as indirect (2) Indirect customers are referred to the Company by introducing brokers Contract Assets and Contract Liabilities The timing of revenue recognition may differ from the timing of payment from customers. The Company records a receivable when revenue is recognized prior to payment, and when the Company has an unconditional right to payment. The Company records a contract liability when payment is received, prior to the time at which the service obligation is satisfied.

FAIR VALUE MEASUREMENT

FAIR VALUE MEASUREMENT	9 Months Ended
	Sep. 30, 2018
Fair Value Disclosures [Abstract]
FAIR VALUE MEASUREMENT	FAIR VALUE INFORMATION Fair value is defined as the price that would be received in exchange for an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. U.S. Generally Accepted Accounting Principles (“US GAAP”) establishes a three level hierarchy that ranks the quality and reliability of information used in developing fair value estimates for financial instruments. The hierarchy gives the highest priority to quoted prices in active markets and the lowest priority to unobservable data. In cases where two or more levels of inputs are used to determine fair value, a financial instrument’s level is determined based on the lowest level input that is considered significant to the fair value measurement in its entirety. The three levels of fair value hierarchy are summarized below: Level 1 - Unadjusted quoted prices in active markets that are accessible at the measurement date for identical, unrestricted assets or liabilities; Level 2 - Quoted prices in markets that are not considered to be active or financial instruments for which all significant inputs are observable, either directly or indirectly; and Level 3 - Valuations that require inputs that are both unobservable to a market participant and significant to the fair value measurement. For assets and liabilities that are transferred between levels during the period, fair values are ascribed as if the assets or liabilities had been transferred as of the beginning of the period. The following table presents the Company’s assets and liabilities that were measured at fair value on a recurring basis during the reporting period and the related hierarchy levels (amounts in thousands): Fair Value Measurements on a Recurring Basis Level 1 Level 2 Level 3 Total Financial Assets/(Liabilities): Cash and cash equivalents: Money market accounts $ 265,260 $ — $ — $ 265,260 Cash and cash equivalents held for customers: US treasury bills: U.S. government and agency securities 103,109 — — 103,109 Receivable from brokers: Broker derivative contracts — (8,148 ) — (8,148 ) Other assets: Certificates of deposit 176 — — 176 Other 119 — — 119 Payables to customers: Customer derivative contracts — 121,174 — 121,174 Payables to brokers: Broker derivative contracts — 3,335 — 3,335 Total $ 368,664 $ 116,361 $ — $ 485,025 Fair Value Measurements on a Recurring Basis Level 1 Level 2 Level 3 Total Financial Assets/(Liabilities): Cash and cash equivalents: Money market accounts $ 219,286 $ — $ — $ 219,286 Cash and cash equivalents held for customers: US treasury bills: U.S. government and agency securities 105,190 — — 105,190 Receivable from brokers: Broker derivative contracts — 4,966 — 4,966 Other assets: Certificates of deposit 175 — — 175 Other 130 — — 130 Payables to customers: Customer derivative contracts — 129,966 — 129,966 Payables to brokers: Broker derivative contracts $ — (3,170 ) $ — (3,170 ) Total $ 324,781 $ 131,762 $ — $ 456,543 The Company has not changed its valuation approaches or techniques in measuring the fair value of any financial assets and liabilities during the nine months ended September 30, 2018 , nor has there been any movement between levels during the period. Level 1 Financial Assets The Company has U.S. Treasury bills, money market accounts and certificates of deposit that are Level 1 financial instruments that are recorded based upon listed or quoted market rates. The U.S. Treasury bills and money market accounts are recorded in Cash and cash equivalents and Cash and cash equivalents held for customers and the certificates of deposit are recorded in Other Assets . Level 2 Financial Assets and Liabilities The Company has customer derivative contracts that are Level 2 financial instruments recorded in Payables to customers. The Company has broker derivative contracts that are Level 2 financial instruments recorded in Receivables from brokers and Payables to brokers. The fair values of these Level 2 financial instruments are based upon directly observable values for underlying instruments. Level 3 Financial Liabilities The Company did not have any Level 3 Financial Assets or Liabilities on September 30, 2018 or December 31, 2017 . 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 sheets (amounts in thousands). Receivables from brokers comprise open trades, which are measured at fair value (disclosed above), and the Company’s posted funds with brokers that are required as collateral for holding trading positions, which are not measured at fair value but approximate fair value. These deposits approximate fair value because they are cash balances that the Company may withdraw at its discretion. Settlement would be expected to occur within a relatively short period of time once a withdrawal is initiated. Payables to customers comprise open trades, which are measured at fair value (disclosed above), and customer deposits that the Company holds for its role as clearing broker. These deposits are not measured at fair value, but approximate fair value, because they are cash balances that the Company or its customers can settle at either party’s discretion. Such settlement would occur within a relatively short period of time once a withdrawal is initiated. Payables to brokers comprise open trades, which are measured at fair value (disclosed above) and cash due to brokers. The cash within this balance is not measured at fair value but does approximate fair value, because it is immediately payable to the brokers. Settlement with brokers generally occurs either on the same or next business day following a margin call. The carrying value of Convertible senior notes represents the notes’ principal amounts net of unamortized discount (refer to Note 14 ). The Company assessed the notes’ fair value as determined by current Company-specific and risk free interest rates as of the balance sheet date. As of September 30, 2018 Fair Value Measurements using: Carrying Value Fair Value Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Financial Assets: Receivables from brokers $ 65,600 $ 65,600 $ — $ 65,600 $ — Financial Liabilities: Payables to customers $ 1,008,456 $ 1,008,456 $ — $ 1,008,456 $ — Payable to brokers $ 5,089 $ 5,089 $ — $ 5,089 $ — Convertible senior notes $ 136,864 $ 164,501 $ — $ 164,501 $ — As of December 31, 2017 Fair Value Measurements using: Carrying Value Fair Value Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Financial Assets: Receivables from brokers $ 73,537 $ 73,537 $ — $ 73,537 $ — Payables to brokers $ 381 $ 381 $ — $ 381 $ — Financial Liabilities: Payables to customers $ 1,108,794 $ 1,108,794 $ — $ 1,108,794 $ — Convertible senior notes $ 132,221 $ 205,073 $ — $ 205,073 $ —

DERIVATIVES

DERIVATIVES	9 Months Ended
	Sep. 30, 2018
Derivative Instruments and Hedging Activities Disclosure [Abstract]
DERIVATIVES	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 brokers, Payables to customers and Payables to brokers on the accompanying Condensed Consolidated Balance Sheets (amounts in thousands): September 30, 2018 Gross amounts of Gross amount of Net amounts of Derivative Instruments: Foreign currency exchange contracts $ 97,454 $ (21,747 ) $ 75,707 CFD contracts 88,122 (54,058 ) 34,064 Metals contracts 8,584 (1,994 ) 6,590 Total $ 194,160 $ (77,799 ) $ 116,361 September 30, 2018 Cash Collateral Net amounts of Net amounts of Derivative Assets/(Liabilities): Receivables from brokers $ 65,600 $ (8,148 ) $ 57,452 Payables to customers $ (1,008,456 ) $ 121,174 $ (887,282 ) Payable to brokers $ (5,089 ) $ 3,335 $ (1,754 ) December 31, 2017 Gross amounts of Gross amount of Net amounts of Derivative Instruments: Foreign currency exchange contracts $ 121,104 $ (31,556 ) $ 89,548 CFD contracts 102,659 (62,322 ) 40,337 Metals contracts 4,084 (2,207 ) 1,877 Total $ 227,847 $ (96,085 ) $ 131,762 December 31, 2017 Cash Collateral Net amounts of Net amounts of Derivative Assets/(Liabilities): Receivables from brokers $ 73,537 $ 4,966 $ 78,503 Payables to customers $ (1,108,794 ) $ 129,966 $ (978,828 ) Payables to brokers $ 381 $ (3,170 ) $ (2,789 ) The Company’s derivatives include different underlyings which vary in price. Foreign exchange contracts typically have prices less than two dollars, while certain metals contracts and CFDs can have considerably higher prices. The amounts reported within Receivables from brokers, Payables to customers, and Payables to brokers on the Condensed Consolidated Balance Sheets are derived from the number of contracts below (amounts in thousands): September 30, 2018 Total contracts in long positions Total contracts in short positions Derivative Instruments: Foreign currency exchange contracts 2,323,419 3,031,582 CFD contracts 109,109 151,645 Metals contracts 87 47 Total 2,432,615 3,183,274 December 31, 2017 Total contracts in long positions Total contracts in short positions Derivative Instruments: Foreign currency exchange contracts 2,075,789 4,148,056 CFD contracts 126,519 174,835 Metals contracts 414 217 Total 2,202,722 4,323,108 The Company did not designate any of its derivatives as hedging instruments. Net gains with respect to derivative instruments reflected in Retail revenue in the accompanying Condensed Consolidated Statements of Operations and Comprehensive Income for the three and nine months ended September 30, 2018 and September 30, 2017 were as follows (amounts in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2018 2017 2018 2017 Derivative Instruments: Foreign currency exchange contracts $ 57,619 $ 30,487 $ 150,484 $ 91,496 CFD contracts 16,298 25,073 68,126 78,286 Metals contracts 8,928 6,583 20,413 10,365 Total $ 82,845 $ 62,143 $ 239,023 $ 180,147

RECEIVABLES FROM BROKERS

RECEIVABLES FROM BROKERS	9 Months Ended
	Sep. 30, 2018
Brokers and Dealers [Abstract]
RECEIVABLES FROM BROKERS	RECEIVABLES FROM BROKERS The Company has posted funds with brokers as collateral required by agreements for holding trading positions. These amounts are reflected as Receivables from brokers on the Condensed Consolidated Balance Sheets. Amounts receivable from brokers consisted of the following as of (amounts in thousands): September 30, 2018 December 31, 2017 Required collateral $ 65,600 $ 73,537 Open foreign exchange positions (8,148 ) 4,966 Total $ 57,452 $ 78,503

PROPERTY AND EQUIPMENT

PROPERTY AND EQUIPMENT	9 Months Ended
	Sep. 30, 2018
Property, Plant and Equipment [Abstract]
PROPERTY AND EQUIPMENT	PROPERTY AND EQUIPMENT Property and equipment, including leasehold improvements and capitalized software development costs, consisted of the following as of (amounts in thousands): September 30, 2018 December 31, 2017 Software $ 59,442 $ 57,047 Computer equipment 13,744 18,390 Leasehold improvements 10,904 11,068 Telephone equipment 656 643 Office equipment 1,945 2,110 Furniture and fixtures 3,324 3,592 Web site development costs 635 386 Gross property and equipment 90,650 93,236 Less: Accumulated depreciation and amortization (57,193 ) (52,494 ) Property and equipment, net $ 33,457 $ 40,742 Depreciation and amortization expense for property and equipment was $4.7 million and $4.4 million for the three months ended September 30, 2018 and 2017 , respectively, and $15.4 million and $12.3 million for the nine months ended September 30, 2018 and 2017 , respectively.

INTANGIBLE ASSETS

INTANGIBLE ASSETS	9 Months Ended
	Sep. 30, 2018
Goodwill and Intangible Assets Disclosure [Abstract]
INTANGIBLE ASSETS	INTANGIBLE ASSETS The Company’s various intangible assets consisted of the following as of (amounts in thousands): September 30, 2018 December 31, 2017 Intangibles Gross Accumulated Net Gross Accumulated Net Customer lists $ 59,213 $ (38,377 ) $ 20,836 $ 60,420 $ (31,698 ) $ 28,722 Technology 49,926 (37,976 ) 11,950 72,204 (43,270 ) 28,934 Trademarks 7,447 (4,401 ) 3,046 7,680 (3,730 ) 3,950 Total finite lived intangibles 116,586 (80,754 ) 35,832 140,304 (78,698 ) 61,606 Trademark not subject to amortization (1) 363 — 363 363 — 363 Total intangibles $ 116,949 $ (80,754 ) $ 36,195 $ 140,667 $ (78,698 ) $ 61,969 (1) These indefinite-life trademarks relate to the forex.com and foreignexchange.com domain names where management determined there was no legal, regulatory or technological limitation on their useful lives. The Company compares the recorded value of the indefinite-life intangible assets to their fair value on an annual basis and whenever circumstances arise that indicate that impairment may have occurred. The Company had the following identifiable intangible assets and weighted average amortization periods as of September 30, 2018 : Intangible Assets Amount (in thousands) Weighted average amortization period Customer lists $ 59,213 7.4 years Technology 49,926 7.2 years Trademarks (1) 7,810 6.7 years Total intangible assets $ 116,949 (1) Trademarks with an indefinite-life, as described above, comprise $0.4 million of the $7.8 million of trademarks. Amortization expense for the purchased intangibles was $3.5 million and $3.5 million for the three months ended September 30, 2018 and 2017 , respectively, and $10.8 million and $10.4 million for the nine months ended September 30, 2018 and 2017 , respectively. On February 7, 2017 , the Company entered into an Asset Purchase Agreement (the “Purchase Agreement”) with Forex Capital Markets L.L.C. (“FXCM”). Pursuant to the terms of the Purchase Agreement, FXCM transferred substantially all of its U.S.-domiciled customer accounts to the Company effective as of February 24, 2017 . The Company paid $7.2 million to FXCM as consideration for the purchased accounts for the full year 2017, which was capitalized within Purchased intangible amortization and amortized on a straight line basis over its two year useful life. Goodwill Goodwill is evaluated for impairment on an annual basis on October 31 and in interim periods when events or changes indicate the carrying value may not be recoverable. As a result of the sale of the GTX ECN business, the Company tested the institutional goodwill for impairment using data as of June 30, 2018 and concluded there was no impairment. The $4.6 million of institutional goodwill was allocated to discontinued operations. The Company operates under two reporting units: retail and futures. There were no additions or impairments to the carrying value of the Company’s goodwill during the nine months ended September 30, 2018 . For the year ended December 31, 2017 , the Company performed a qualitative analysis to determine whether it was more likely than not that the fair value of its reporting units was less than their carrying value. As a result of this assessment, the Company determined that it was not necessary to perform a quantitative impairment test and concluded that goodwill assigned to each of its reporting units was not impaired at December 31, 2017 . As of September 30, 2018 and December 31, 2017 , the Company had recorded goodwill of approximately $28.0 million and $33.0 million , respectively. The decrease of $5.0 million was primarily related to the discontinued operations of GTX. The following represents the changes in the carrying amount of goodwill by segment (amounts in thousands): Retail Institutional Futures Total Carrying amount of goodwill as of December 31, 2017 $ 25,952 $ 4,650 $ 2,434 $ 33,036 Foreign currency translation adjustments (313 ) (34 ) (29 ) (376 ) Discontinued operations — (4,616 ) — (4,616 ) Carrying amount of goodwill as of September 30, 2018 $ 25,639 $ — $ 2,405 $ 28,044

OTHER ASSETS

OTHER ASSETS	9 Months Ended
	Sep. 30, 2018
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
OTHER ASSETS	OTHER ASSETS Other assets consisted of the following as of (amounts in thousands): September 30, 2018 December 31, 2017 Vendor and security deposits $ 6,943 $ 11,923 Income tax receivable — 2,132 Deferred tax assets, net 12,563 10,698 GTX trade receivables 178 5,758 Customer debit positions 4,526 2,384 Allowance on customer debit positions (3,532 ) (1,959 ) Prepaid assets 11,490 9,523 Miscellaneous receivables 4,930 4,872 Deferred commitment fees 391 550 Total other assets $ 37,489 $ 45,881

RELATED PARTY TRANSACTIONS

RELATED PARTY TRANSACTIONS	9 Months Ended
	Sep. 30, 2018
Related Party Transactions [Abstract]
RELATED PARTY TRANSACTIONS	RELATED PARTY TRANSACTIONS Certain officers and directors of the Company have personal funds on deposit in separate customer accounts with the Company. These accounts are recorded in Payables to customers on the Condensed Consolidated Balance Sheets. The aggregate amount of these funds was $0.2 million at each of September 30, 2018 and December 31, 2017 . IPGL Limited, the majority selling shareholder in the acquisition of City Index, has a trading account with the Company which is recorded in Payables to customers on the Condensed Consolidated Balance Sheets. The aggregate amount of these funds was $12.4 million and $15.9 million as of September 30, 2018 and December 31, 2017 , respectively. The net revenue generated by any individual related party was not deemed to be material in any period.

NON-CONTROLLING INTERESTS

NON-CONTROLLING INTERESTS	9 Months Ended
	Sep. 30, 2018
Noncontrolling Interest [Abstract]
NON-CONTROLLING INTERESTS	NON-CONTROLLING INTERESTS Non-controlling interests In March 2014, the Company acquired controlling interests in Global Asset Advisors (“GAA”) and Top Third (“TT”). The Company purchased 55% of each entity, and the respective sellers maintained a 45% interest in each entity, subject to immediately exercisable call options for the Company to purchase the remaining interests, as well as put options for the sellers to sell their remaining interests in each entity to the Company that were to become exercisable in 2017. In December 2016, the Company acquired an additional 24% of each entity and, accordingly, the respective sellers now maintain a 21% interest in each entity. In connection with the purchase of these additional interests, the Company and the respective sellers agreed that neither would exercise the call options or put options with respect to the remaining interests prior to December 31, 2017 . In December 2017, the Company and the sellers of TT extended their agreement that neither would exercise the relevant call options or put options through December 31, 2018. In February 2018, the minority owners of GAA notified the Company that they were exercising their put option with respect to their combined 21% ownership of GAA. In September 2018, the Company settled its purchase of the minority ownership interests in GAA for approximately $2.9 million . In accordance with ASC 480-10-S99-3A, Classification and Measurement of Redeemable Securities , non-controlling interests are classified outside of permanent equity as their redemption is not (i) mandatory, (ii) at fixed prices, and (iii) exclusively within the Company’s control. The non-controlling interest related to TT is not classified as a liability, because redemption is not mandatory or at a fixed price. It is not classified as equity because the redemption is not exclusively in the Company’s control. Therefore, the non-controlling interest is held in temporary equity in the Condensed Consolidated Balance Sheets. The non-controlling interests’ carrying value is determined by the Company’s purchase prices and the non-controlling interests’ share of the Company’s subsequent net income. This value is benchmarked against the redemption value of the sellers’ put options. The carrying value is adjusted to the latter, provided that it does not fall below the initial carrying values, as determined by the Company’s purchase price allocation. The Company reflects any changes caused by such an adjustment in retained earnings, rather than in current earnings. The table below reflects the non-controlling interests’ effects on the Company’s financial statements (amounts in thousands): Redeemable non-controlling interests January 1, 2018 $ 4,411 Adjustment to the redemption value of non-controlling interests 901 Net income attributable to non-controlling interests 638 Distributions to non-controlling interest holders (553 ) Purchase of additional shares of non-controlling interest (2,854 ) September 30, 2018 $ 2,543

REVOLVING CREDIT ARRANGEMENT

REVOLVING CREDIT ARRANGEMENT	9 Months Ended
	Sep. 30, 2018
Debt Disclosure [Abstract]
REVOLVING CREDIT ARRANGEMENT	REVOLVING CREDIT ARRANGEMENT On August 3, 2017 , the Company entered into a Credit Agreement, dated as of August 2, 2017 , for a three year U.S. $50.0 million senior secured first lien revolving credit facility that matures in August 2020. Upon request of the Company, the credit facility may be increased by up to $25.0 million , with a minimum increase of $5.0 million . The credit facility contains covenants that are customary for an issuer with senior debt. The commitment fees of $0.4 million is amortized over the life of the facility and is recorded to Other Assets . As of September 30, 2018 , the Company was in compliance with the covenants for its credit facility. As of September 30, 2018 , there were no amounts outstanding under the revolving line of credit.

CONVERTIBLE SENIOR NOTES

CONVERTIBLE SENIOR NOTES	9 Months Ended
	Sep. 30, 2018
Debt Disclosure [Abstract]
CONVERTIBLE SENIOR NOTES	CONVERTIBLE SENIOR NOTES Convertible Senior Notes due 2022 On August 22, 2017 , the Company issued $92.0 million aggregate principal amount of its 5.00% Convertible Senior Notes due 2022 , in a private offering to qualified institutional buyers pursuant to Rule 144A under the Securities Act of 1933, as amended. The Notes bear interest at a fixed rate of 5.00% per year, payable semi-annually in arrears on February 15 and August 15 of each year. The Notes are convertible into cash, shares of the Company’s common stock, or a combination thereof, at the Company’s election. The Company currently intends to settle the debt in cash. The Notes will mature on August 15, 2022 , unless earlier converted, redeemed or repurchased. The Company may not redeem the Notes prior to August 15, 2020 . The net proceeds from the offering were approximately $89.0 million , after deducting discounts to the initial purchasers but prior to other offering expenses payable by the Company. Convertible Senior Notes due 2020 On April 1, 2015 , as part of the City Index acquisition consideration, the Company issued to the sellers $60.0 million aggregate principal amount of 4.125% Convertible Senior Notes maturing on April 1, 2020 . These Convertible Senior Notes pay interest semi-annually on April 1 and October 1 at a rate of 4.125% per year, which commenced on October 1, 2015 . The Company currently intends to settle the debt in cash upon maturity. Convertible Senior Notes due 2018 On November 27 , 2013 , the Company issued $80.0 million principal amount of 4.125% Convertible Senior Notes due December 1, 2018 . The Company received net proceeds of $77.9 million , after deducting the initial purchasers' discount. These Convertible Senior Notes pay interest semi-annually on June 1 and December 1 at a rate of 4.125% per year, which commenced on June 1, 2014 . During the first quarter of 2016 , the Company repurchased $1.9 million in principal amount of the convertible senior notes due 2018, for an aggregate purchase price of $1.7 million . During the third quarter of 2017, the Company repurchased $71.8 million in principal amount of the convertible senior notes due 2018, for an aggregate purchase price of $73.7 million with the proceeds from the issuance of Convertible Senior Notes due 2022. As a result, the Company recognized an extinguishment loss of $4.9 million . The Company currently intends to settle the remaining outstanding debt in cash upon maturity. U.S. GAAP requires an entity to separately account for the liability and equity components of a convertible debt instrument that may be settled entirely or partially in cash upon conversion. The separate accounting must reflect the issuer’s economic interest cost. The balances of the liability and equity components as of September 30, 2018 and December 31, 2017 were as follows (amounts in thousands): September 30, 2018 December 31, 2017 Liability component - principal $ 158,350 $ 158,350 Deferred bond discount (21,069 ) (25,624 ) Deferred financing cost (417 ) (505 ) Liability component - net carrying value $ 136,864 $ 132,221 Additional paid in capital $ 39,405 $ 39,405 Discount attributable to equity (826 ) (826 ) Equity component $ 38,579 $ 38,579 Interest expense related to the Convertible Senior Notes, included in Interest Expense on long term borrowings in the Condensed Consolidated Statements of Operations and Comprehensive Income , was as follows (amounts in thousands): For the Three Months Ended September 30, For the Nine Months Ended September 30, 2018 2017 2018 2017 Interest expense - stated coupon rate $ 1,834 $ 1,701 $ 5,503 $ 4,551 Interest expense - amortization of deferred bond discount and costs 1,570 1,284 4,629 3,793 Total interest expense - convertible senior notes $ 3,404 $ 2,985 $ 10,132 $ 8,344

EARNINGS_(LOSS) PER COMMON SHAR

EARNINGS/(LOSS) PER COMMON SHARE	9 Months Ended
	Sep. 30, 2018
Earnings Per Share [Abstract]
EARNINGS/(LOSS) PER COMMON SHARE	EARNINGS/(LOSS) PER COMMON SHARE Basic and diluted earnings/(loss) per common share are computed by dividing net income/(loss) by the weighted average number of common shares outstanding during the period. Diluted earnings/(loss) 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, unvested restricted stock units and unvested restricted stock awards. Approximately 0.4 million stock options were excluded from the calculation of diluted earnings per share for the three and nine months ended September 30, 2018 , respectively, as they were anti-dilutive. Approximately 0.6 million and 0.6 million stock options were excluded from the calculation of diluted earnings per share for the three and nine months ended September 30, 2017 , respectively, as they were anti-dilutive. Diluted earnings (loss) per share excludes any shares of Company common stock potentially issuable under the Company’s convertible senior notes, which are discussed in Note 14 . Based upon an assumed trading price of $13 for each share of the Company’s common stock, and if the relevant conditions under the indenture governing the 2018 , 2020 , and 2022 convertible senior notes were satisfied, there would be no additional dilutive shares for the 2018 note and an additional 1.5 million and 4.2 million dilutive shares as of September 30, 2018 , for the 2020 and 2022 notes, respectively. The following table sets forth the computation of earnings/(loss) 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, 2018 2017 2018 2017 Net income/(loss) from continuing operations $ 9,969 $ (3,080 ) $ 28,715 $ (8,026 ) Less income attributable to non-controlling interests $ 137 $ 225 $ 638 $ 463 Net income/(loss) from continuing operations $ 9,832 $ (3,305 ) $ 28,077 $ (8,489 ) Adjustment (1) (10 ) 728 (901 ) 1,711 Net income/(loss) available to GAIN common shareholders from continuing operations $ 9,822 $ (2,577 ) $ 27,176 $ (6,778 ) Net income from discontinued operations 2,344 725 67,330 977 Weighted average common shares outstanding: Basic weighted average common shares outstanding 44,553,903 46,323,038 44,787,875 47,295,843 Effect of dilutive securities: Stock options 238,172 206,964 258,934 247,575 RSUs/RSAs 192,646 — 223,988 4,615 Diluted weighted average common shares outstanding 44,984,721 46,323,038 45,270,797 47,295,843 Basic earnings/(loss) from continuing operations $ 0.22 $ (0.06 ) $ 0.61 $ (0.14 ) Basic earnings from discontinued operations $ 0.05 $ 0.02 $ 1.50 $ 0.02 Diluted earnings/(loss) from continuing operations $ 0.22 $ (0.06 ) $ 0.60 $ (0.14 ) Diluted earnings from discontinued operations $ 0.05 $ 0.02 $ 1.49 $ 0.02 (1) During the three and nine months ended September 30, 2018 and 2017 , the Company concluded that the carrying value of the Company's redeemable noncontrolling interests was less than their redemption value, requiring that an adjustment to the carrying value be recorded for purposes of calculating earnings/(loss) per common share. The adjustment to increase or reduce the carrying value will, respectively, reduce or increase earnings/(loss) per common share by reducing or increasing net income available to common shareholders.

COMMITMENT AND CONTINGENCIES

COMMITMENT AND CONTINGENCIES	9 Months Ended
	Sep. 30, 2018
Commitments and Contingencies Disclosure [Abstract]
COMMITMENT AND CONTINGENCIES	COMMITMENT AND CONTINGENCIES 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 reasonably 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 can be reasonably estimated for any proceeding. The Company recorded a contingent provision for the three months ended September 30, 2018 which relates to an ongoing contractual dispute with a service provider relating to the historical deployment of software supporting one of our legacy trading platforms. This amount is reflected within Contingent provision on the Condensed Consolidated Statement of Operations and Comprehensive Income.

INCOME TAXES

INCOME TAXES	9 Months Ended
	Sep. 30, 2018
Income Tax Disclosure [Abstract]
INCOME TAXES	INCOME TAXES The Company's provision s for income taxes were approximately $4.0 million and $11.4 million , respectively, for the three and nine months ended September 30, 2018 and a provision /(benefit) of approximately $0.1 million and $(4.3) million for the three and nine months ended September 30, 2017 . These amounts reflect the Company's estimate of the annual effective tax rates of 28.5% and (3.3)% , adjusted for certain discrete items, for the three months ended September 30, 2018 and 2017 , respectively. The Company's effective tax rates of 28.4% and 35.2% for the nine months ended September 30, 2018 and 2017 , respectively, reflect the Company's estimate of the annual effective tax rate adjusted for certain discrete items, primarily changes in uncertain tax positions. Changes in the Company's effective tax rate arise primarily from changes in the geographic mix of revenues and expenses, as well as changes to statutory tax rates. 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. Certain net deferred tax assets of the Company are included in Other assets on the Condensed Consolidated Balance Sheets.

REGULATORY REQUIREMENTS

REGULATORY REQUIREMENTS	9 Months Ended
	Sep. 30, 2018
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, 2018 and the actual amounts of capital that were maintained (amounts in millions): Entity Name Minimum Capital Excess Percent of GAIN Capital Group, LLC $ 34.3 $ 51.9 $ 17.6 151 % GAIN Capital Securities, Inc. 0.1 0.4 0.3 400 % GAIN Capital U.K., Ltd. 69.1 198.5 129.4 287 % GAIN Capital Japan Co., Ltd. 1.4 9.7 8.3 693 % GAIN Capital Australia, Pty. Ltd. 0.7 5.7 5.0 814 % GAIN Capital-Forex.com Hong Kong, Ltd. 1.9 3.7 1.8 195 % GAIN Global Markets, Inc. 0.7 1.3 0.6 186 % GAIN Capital-Forex.com Canada, Ltd. 0.2 1.5 1.3 750 % GAIN Capital Singapore Pte., Ltd. 0.4 8.1 7.7 2,025 % Trade Facts, Ltd. 0.6 3.5 2.9 583 % Global Asset Advisors, LLC 0.0 2.2 2.2 100 % GTX SEF, LLC 0.7 0.9 0.2 129 % Total $ 110.1 $ 287.4 $ 177.3 261 %

SEGMENT INFORMATION

SEGMENT INFORMATION	9 Months Ended
	Sep. 30, 2018
Segment Reporting [Abstract]
SEGMENT INFORMATION	SEGMENT INFORMATION ASC Topic 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 which engage in business activities from which they may earn revenues and incur expenses and 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) the reported profit or loss in absolute amount of which 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. During the first quarter of 2018, the Company completed its implementation of global support groups in the areas of finance, legal, human resources, and treasury. These groups are now centrally managed and support all business functions. Therefore, all costs related to these groups previously recorded within the retail segment will now be classified in our corporate and other segment to better align the cost reporting with the support services. The change in segment reporting has no impact on the net profit or loss of the Company. To enable comparisons with prior period performance, historical segment information for the periods included in the tables below reflect this reporting change. On June 29, 2018, the Company completed the sale of its GTX ECN business, which previously comprised the Company's institutional segment, to Deutsche Börse Group via its FX unit, 360T, for a total purchase price of $100 million less a working capital adjustment which amounted to a $0.2 million reduction in purchase price. The Company determined that the institutional segment met the discontinued operations criteria set forth in ASC Subtopic 205-20-45, Presentation of Financial Statements , in the quarter ended June 30, 2018. As such, the institutional segment results have been classified as discontinued operations in the accompanying Condensed Consolidated Statements of Operations and Comprehensive Income. For more information relating to the discontinued operations of the Company's GTX ECN business, please see Note 3 . Retail Segment Business in the retail segment is conducted primarily through the Company’s FOREX.com and City Index brands. The Company provides its retail customers around the world with access to over 12,500 global financial markets, including spot forex, precious metals, and CFDs on currencies, commodities, indices, individual equities, cryptocurrencies, bonds and interest rate products, as well as OTC options on forex. In the United Kingdom, the Company also offer spread bets, which are investment products similar to CFDs, but that offer more favorable tax treatment to residents of that country. Futures Segment The futures segment offers execution and related services for exchange-traded futures, including futures on Bitcoin, and futures options on major U.S. and European exchanges. The Company offers futures services through its subsidiary, GAIN Capital Group, LLC, under several brands, including GAIN Capital Futures. In addition, in 2014, the Company expanded its futures business by acquiring majority interests in GAA and TT. Corporate and other Corporate and other provides general corporate services to the Company’s segments. Corporate and other revenue primarily comprises foreign currency transaction gains and losses. Selected financial information by segment is presented in the following tables (amounts in thousands): Retail Three Months Ended September 30, Nine Months Ended September 30, 2018 2017 2018 2017 Net revenue $ 85,856 $ 63,927 $ 246,060 $ 184,619 Employee compensation and benefits 14,355 12,726 43,427 40,466 Selling and marketing 9,957 6,280 22,117 22,429 Referral fees 5,321 9,796 20,047 31,945 Other operating expenses 17,194 15,634 53,206 44,253 Segment profit $ 39,029 $ 19,491 $ 107,263 $ 45,526 Futures Three Months Ended September 30, Nine Months Ended September 30, 2018 2017 2018 2017 Net revenue $ 9,737 $ 9,777 $ 33,328 $ 30,757 Employee compensation and benefits 2,416 2,327 7,790 7,372 Selling and marketing 181 121 625 607 Referral fees 2,827 3,128 9,996 10,732 Other operating expenses 3,043 2,904 10,392 9,879 Segment profit $ 1,270 $ 1,297 $ 4,525 $ 2,167 Corporate and Other Three Months Ended September 30, Nine Months Ended September 30, 2018 2017 2018 2017 Other revenue/(loss) $ (52 ) $ 56 $ (1,302 ) $ 155 Employee compensation and benefits 6,082 5,758 18,447 16,507 Selling and marketing 77 1 211 118 Other operating expenses 3,581 2,202 10,550 7,438 Loss $ (9,792 ) $ (7,905 ) $ (30,510 ) $ (23,908 ) Reconciliation of operating segment profit to Income before income tax expense Three Months Ended September 30, Nine Months Ended September 30, 2018 2017 2018 2017 Retail segment $ 39,029 $ 19,491 $ 107,263 $ 45,526 Futures segment 1,270 1,297 4,525 2,167 Corporate and other (9,792 ) (7,905 ) (30,510 ) (23,908 ) SEGMENT PROFIT 30,507 12,883 81,278 23,785 Depreciation and amortization 4,685 4,373 15,394 12,322 Purchased intangible amortization 3,504 3,524 10,784 10,407 Restructuring expenses — — 25 — Contingent provision 4,975 — 4,975 — Impairment of investment — — (130 ) — OPERATING PROFIT 17,343 4,986 50,230 1,056 Interest expense on long term borrowings 3,404 2,985 10,132 8,344 Loss on extinguishment of debt — 4,944 $ — $ 4,944 INCOME/(LOSS) BEFORE INCOME TAX EXPENSE $ 13,939 $ (2,943 ) $ 40,098 $ (12,232 )

SUBSEQUENT EVENTS

SUBSEQUENT EVENTS	9 Months Ended
	Sep. 30, 2018
Subsequent Events [Abstract]
SUBSEQUENT EVENTS	SUBSEQUENT EVENTS On October 9, 2018, the Company announced a “modified Dutch auction” tender offer to purchase up to $50 million of shares of its common stock, or such lesser number of shares of its common stock as are properly tendered and not properly withdrawn, at a price not less than $7.24 nor greater than $7.94 per share of common stock, to the seller in cash, less any applicable withholding taxes and without interest (the “Offer”). The Offer is made upon the terms and subject to the conditions described in the offer to purchase and in the related letter of transmittal, each of which are attached as exhibits to the Company's Schedule TO, as filed with the SEC on October 9, 2018. On October 25, 2018 , the Company announced the payment of a $0.06 dividend per share of Common Stock payable on December 18, 2018 to stockholders of record on December 11, 2018 .

DESCRIPTION OF BUSINESS AND B_2

DESCRIPTION OF BUSINESS AND BASIS OF PRESENTATION (Policies)	9 Months Ended
	Sep. 30, 2018
Accounting Policies [Abstract]
Basis of Presentation and Principles of Consolidation	The accompanying unaudited Condensed Consolidated Financial Statements reflect all adjustments that, in the opinion of management, are necessary for a fair presentation of the financial statements for the interim periods. The financial statements are presented in accordance with accounting principles generally accepted in the United States of America (“U.S. GAAP”). The unaudited Condensed Consolidated Financial Statements have been prepared in accordance with the Securities and Exchange Commission's (“SEC”) regulations 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 audited Consolidated Financial Statements and related notes included in the Company’s Annual Report on Form 10-K as of and for the year ended December 31, 2017 . The unaudited Condensed Consolidated Financial Statements include the accounts of the Company and its wholly-owned subsidiaries, after the elimination of inter-company transactions and balances.
Accounting Pronouncements Recently Adopted and Not Yet Adopted	ACCOUNTING PRONOUNCEMENTS Recently Adopted In January 2017, the Financial Accounting Standards Board (the “FASB”) issued ASU No. 2017-04, “Intangibles-Goodwill and Other (Topic 350): Simplifying the Test for Goodwill Impairment,” which eliminates the requirement to calculate the implied fair value of goodwill to measure a goodwill impairment charge (Step 2) from the goodwill impairment test. Instead, an impairment charge will equal the amount by which a reporting unit’s carrying amount exceeds its fair value, not to exceed the amount of goodwill allocated to the reporting unit. The guidance will be effective for the Company for its annual or any interim goodwill impairment tests in fiscal years beginning after December 15, 2019, with early adoption permitted after January 1, 2017 . The Company has adopted this ASU as of January 1, 2018, and will apply Step 2 going forward to the extent it is required. In November 2016, the FASB issued ASU No. 2016-18, “Restricted Cash,” which requires that companies present cash, cash equivalents and amounts generally described as restricted cash or restricted cash equivalents (restricted cash) when reconciling beginning-of-period and end-of-period totals on the Statement of Cash Flows. The Company has retrospectively adopted this ASU as of January 1, 2018 and includes cash and cash equivalents held for customers as restricted cash. As a result, Net cash provided by operating activities on the Statement of Cash Flows decreased by $18.5 million for the nine months ended September 30, 2017. The Company defines restricted cash to include cash and cash equivalents held for customers, which represents cash and other highly liquid assets held to fund customer liabilities in connection with trading positions. Included in this balance are funds deposited by customers and funds accruing to customers as a result of trades or contracts. The Company records a corresponding liability in connection with this amount in Payables to customers. In addition, the Company holds certain customer funds in segregated or secured broker accounts. Legally segregated balances are not available for general use, in accordance with certain jurisdictional regulatory requirements. In May 2014, the FASB issued ASU No. 2014-09, “Revenue from Contracts with Customers”, which is part of ASC Topic 606. It defines how companies report revenues from contracts with customers and also requires certain enhanced disclosures. The standard’s provisions and related amendments are effective for annual reporting periods beginning after December 15, 2017. On January 1, 2018, the Company adopted this guidance, which did not have a material impact on the Company’s financial statements. A substantial portion of revenue falls under ASC Topic 825, Financial Instruments, which is excluded from the scope of the new guidance. The Company adopted ASU No. 2014-09 using the modified retrospective approach. See Note 4 Revenue Recognition for additional disclosure. Not Yet Adopted In February 2016, the FASB issued ASU No. 2016-02, “Leases (Topic 842),” which amended the guidance on accounting for leases. The FASB issued this update to increase transparency and comparability among organizations. This update requires recognizing lease assets and lease liabilities on the balance sheet and disclosing key information about leasing arrangements. The guidance is effective for fiscal years beginning after December 15, 2018 , including interim periods within that fiscal year. We are in the process of collecting and reviewing leases that have been entered into by the Company within the scope of ASC 842, including potential disclosures, in order to complete our evaluation of the impact of the standard on our consolidated financial statements prior to the end of 2018. In addition, we continue to monitor additional changes, modifications, clarifications or interpretations undertaken by the FASB or others, which may impact our current conclusions. We will adopt the requirements of the new standard effective January 1, 2019. In February 2018, the FASB issued ASU No. 2018-02, “Income Statement - Reporting Comprehensive Income (Topic 220),” to address certain income tax effects in Accumulated Other Comprehensive Income (AOCI) resulting from the tax reform enacted in 2017. The amended guidance provides an option to reclassify tax effects within AOCI to retained earnings in the period in which the effect of the tax reform is recorded. The amendments are effective for fiscal years beginning after December 15, 2018 , including interim periods. Early adoption is permitted. This will not have an impact on the Company as there are no balances in AOCI that are tax effected.
Revenue Recognition	In May 2014, the FASB issued ASU No. 2014-09, “Revenue from Contracts with Customers”, which is part of ASC Topic 606. It defines how companies report revenues from contracts with customers and also requires certain enhanced disclosures. The standard’s provisions and related amendments are effective for annual reporting periods beginning after December 15, 2017. On January 1, 2018, the Company adopted this guidance, which did not have a material impact on the Company’s financial statements. A substantial portion of the Company's retail revenue as well as interest revenue falls under ASC Topic 825, “Financial Instruments”, which is excluded from the scope of Topic 606. Additionally, the Company’s futures segment revenue was not materially impacted as the satisfaction of performance obligations under the new guidance is materially consistent with the Company’s previous revenue recognition policies. Accordingly, the adoption of the new standard did not result in a transition adjustment to opening retained earnings, and as a result, revenues for contracts with customers would not have been adjusted in prior periods and are not presented herein on an adjusted basis. Similarly, the amended guidance did not have a material impact on the recognition of costs incurred to obtain new contracts. As a result of the adoption of the new guidance, the Company recorded a gross up of $1.0 million for the nine months ended September 30, 2018 which impacted referral fee expense in the Company's discontinued operations. There was no gross up required for the three months ended September 30, 2018 . The Company adopted ASU No. 2014-09 using the modified retrospective approach. Under ASC Topic 606, revenues are recognized when control of the promised goods or services is transferred to customers in exchange for an amount that reflects the consideration the Company expects to be entitled to in transferring those goods or services. The following is a description of the Company’s revenue recognition policies as they relate to revenue from contracts with customers. Futures Revenue Futures revenue consists primarily of commissions earned on futures and futures options trades. The Company acts as an agent for the trades executed in our futures segment and are not exposed to market risk in connection with that activity. The Company earns commission revenue by acting as an agent on behalf of customers. The Company’s futures revenue performance obligations also consist of trade execution and are satisfied on the trade date; accordingly, commission revenues are recorded on the trade date.

DISCONTINUED OPERATIONS (Tables

DISCONTINUED OPERATIONS (Tables)	9 Months Ended
	Sep. 30, 2018
Discontinued Operations and Disposal Groups [Abstract]
Disposal Groups, Including Discontinued Operations	The results of operations from the discontinued segment for the three and nine months ended September 30, 2018 are as follows (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2018 2017 2018 2017 REVENUE: Institutional revenue $ — $ 7,520 $ 16,379 $ 23,322 Other revenue/(loss) — — (2 ) — Total non-interest revenue — 7,520 16,377 23,322 Interest revenue — 33 103 81 Total net interest revenue — 33 103 81 Net revenue $ — $ 7,553 $ 16,480 $ 23,403 EXPENSES: Employee compensation and benefits $ 94 $ 2,993 $ 5,973 $ 9,999 Trading expenses — 2,409 5,439 7,320 Other expenses 30 1,104 3,955 4,287 Total operating expense 124 6,506 15,367 21,606 OPERATING PROFIT/(LOSS) (124 ) 1,047 1,113 1,797 Gain/(loss) on sale of discontinued operations (142 ) — 69,439 — INCOME/(LOSS) BEFORE INCOME TAX EXPENSE/(BENEFIT) (266 ) 1,047 70,552 1,797 Income tax expense/(benefit) (2,610 ) 322 3,222 820 NET INCOME FROM DISCONTINUED OPERATIONS $ 2,344 $ 725 $ 67,330 $ 977

REVENUE RECOGNITION (Tables)

REVENUE RECOGNITION (Tables)	9 Months Ended
	Sep. 30, 2018
Revenue from Contract with Customer [Abstract]
Disaggregation of Revenue	The following table presents the Company’s revenue from contracts with customers disaggregated by the services described above for the futures segment for the three and nine months ended September 30, 2018 : Three months ended September 30, 2018 Nine months ended September 30, 2018 Futures Direct Customers (1) $ 2,106 $ 7,272 Indirect Customers (2) 5,270 18,854 Other 2,361 7,202 Total Segment Revenue $ 9,737 $ 33,328 (1) Direct customers are all customers not classified as indirect (2) Indirect customers are referred to the Company by introducing brokers

FAIR VALUE MEASUREMENT (Tables)

FAIR VALUE MEASUREMENT (Tables)	9 Months Ended
	Sep. 30, 2018
Fair Value Disclosures [Abstract]
Assets and Liabilities Measured at Fair Value on Recurring Basis	The following table presents the Company’s assets and liabilities that were measured at fair value on a recurring basis during the reporting period and the related hierarchy levels (amounts in thousands): Fair Value Measurements on a Recurring Basis Level 1 Level 2 Level 3 Total Financial Assets/(Liabilities): Cash and cash equivalents: Money market accounts $ 265,260 $ — $ — $ 265,260 Cash and cash equivalents held for customers: US treasury bills: U.S. government and agency securities 103,109 — — 103,109 Receivable from brokers: Broker derivative contracts — (8,148 ) — (8,148 ) Other assets: Certificates of deposit 176 — — 176 Other 119 — — 119 Payables to customers: Customer derivative contracts — 121,174 — 121,174 Payables to brokers: Broker derivative contracts — 3,335 — 3,335 Total $ 368,664 $ 116,361 $ — $ 485,025 Fair Value Measurements on a Recurring Basis Level 1 Level 2 Level 3 Total Financial Assets/(Liabilities): Cash and cash equivalents: Money market accounts $ 219,286 $ — $ — $ 219,286 Cash and cash equivalents held for customers: US treasury bills: U.S. government and agency securities 105,190 — — 105,190 Receivable from brokers: Broker derivative contracts — 4,966 — 4,966 Other assets: Certificates of deposit 175 — — 175 Other 130 — — 130 Payables to customers: Customer derivative contracts — 129,966 — 129,966 Payables to brokers: Broker derivative contracts $ — (3,170 ) $ — (3,170 ) Total $ 324,781 $ 131,762 $ — $ 456,543
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	The carrying value of Convertible senior notes represents the notes’ principal amounts net of unamortized discount (refer to Note 14 ). The Company assessed the notes’ fair value as determined by current Company-specific and risk free interest rates as of the balance sheet date. As of September 30, 2018 Fair Value Measurements using: Carrying Value Fair Value Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Financial Assets: Receivables from brokers $ 65,600 $ 65,600 $ — $ 65,600 $ — Financial Liabilities: Payables to customers $ 1,008,456 $ 1,008,456 $ — $ 1,008,456 $ — Payable to brokers $ 5,089 $ 5,089 $ — $ 5,089 $ — Convertible senior notes $ 136,864 $ 164,501 $ — $ 164,501 $ — As of December 31, 2017 Fair Value Measurements using: Carrying Value Fair Value Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Financial Assets: Receivables from brokers $ 73,537 $ 73,537 $ — $ 73,537 $ — Payables to brokers $ 381 $ 381 $ — $ 381 $ — Financial Liabilities: Payables to customers $ 1,108,794 $ 1,108,794 $ — $ 1,108,794 $ — Convertible senior notes $ 132,221 $ 205,073 $ — $ 205,073 $ —

DERIVATIVES (Tables)

DERIVATIVES (Tables)	9 Months Ended
	Sep. 30, 2018
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Fair Values of Derivative Instruments	The table below represents the fair values of the Company’s derivative instruments reported within Receivables from brokers, Payables to customers and Payables to brokers on the accompanying Condensed Consolidated Balance Sheets (amounts in thousands): September 30, 2018 Gross amounts of Gross amount of Net amounts of Derivative Instruments: Foreign currency exchange contracts $ 97,454 $ (21,747 ) $ 75,707 CFD contracts 88,122 (54,058 ) 34,064 Metals contracts 8,584 (1,994 ) 6,590 Total $ 194,160 $ (77,799 ) $ 116,361 September 30, 2018 Cash Collateral Net amounts of Net amounts of Derivative Assets/(Liabilities): Receivables from brokers $ 65,600 $ (8,148 ) $ 57,452 Payables to customers $ (1,008,456 ) $ 121,174 $ (887,282 ) Payable to brokers $ (5,089 ) $ 3,335 $ (1,754 ) December 31, 2017 Gross amounts of Gross amount of Net amounts of Derivative Instruments: Foreign currency exchange contracts $ 121,104 $ (31,556 ) $ 89,548 CFD contracts 102,659 (62,322 ) 40,337 Metals contracts 4,084 (2,207 ) 1,877 Total $ 227,847 $ (96,085 ) $ 131,762 December 31, 2017 Cash Collateral Net amounts of Net amounts of Derivative Assets/(Liabilities): Receivables from brokers $ 73,537 $ 4,966 $ 78,503 Payables to customers $ (1,108,794 ) $ 129,966 $ (978,828 ) Payables to brokers $ 381 $ (3,170 ) $ (2,789 )
Notional Values of Derivative Instruments	The amounts reported within Receivables from brokers, Payables to customers, and Payables to brokers on the Condensed Consolidated Balance Sheets are derived from the number of contracts below (amounts in thousands): September 30, 2018 Total contracts in long positions Total contracts in short positions Derivative Instruments: Foreign currency exchange contracts 2,323,419 3,031,582 CFD contracts 109,109 151,645 Metals contracts 87 47 Total 2,432,615 3,183,274 December 31, 2017 Total contracts in long positions Total contracts in short positions Derivative Instruments: Foreign currency exchange contracts 2,075,789 4,148,056 CFD contracts 126,519 174,835 Metals contracts 414 217 Total 2,202,722 4,323,108
Net Gains (Losses) With Respect to Derivative Instruments Which are Reflected in Trading Revenue	Net gains with respect to derivative instruments reflected in Retail revenue in the accompanying Condensed Consolidated Statements of Operations and Comprehensive Income for the three and nine months ended September 30, 2018 and September 30, 2017 were as follows (amounts in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2018 2017 2018 2017 Derivative Instruments: Foreign currency exchange contracts $ 57,619 $ 30,487 $ 150,484 $ 91,496 CFD contracts 16,298 25,073 68,126 78,286 Metals contracts 8,928 6,583 20,413 10,365 Total $ 82,845 $ 62,143 $ 239,023 $ 180,147

RECEIVABLES FROM BROKERS (Table

RECEIVABLES FROM BROKERS (Tables)	9 Months Ended
	Sep. 30, 2018
Brokers and Dealers [Abstract]
Schedule of Receivable from Brokers	Amounts receivable from brokers consisted of the following as of (amounts in thousands): September 30, 2018 December 31, 2017 Required collateral $ 65,600 $ 73,537 Open foreign exchange positions (8,148 ) 4,966 Total $ 57,452 $ 78,503

PROPERTY AND EQUIPMENT (Tables)

PROPERTY AND EQUIPMENT (Tables)	9 Months Ended
	Sep. 30, 2018
Property, Plant and Equipment [Abstract]
Schedule of Property and Equipment	Property and equipment, including leasehold improvements and capitalized software development costs, consisted of the following as of (amounts in thousands): September 30, 2018 December 31, 2017 Software $ 59,442 $ 57,047 Computer equipment 13,744 18,390 Leasehold improvements 10,904 11,068 Telephone equipment 656 643 Office equipment 1,945 2,110 Furniture and fixtures 3,324 3,592 Web site development costs 635 386 Gross property and equipment 90,650 93,236 Less: Accumulated depreciation and amortization (57,193 ) (52,494 ) Property and equipment, net $ 33,457 $ 40,742

INTANGIBLE ASSETS (Tables)

INTANGIBLE ASSETS (Tables)	9 Months Ended
	Sep. 30, 2018
Goodwill and Intangible Assets Disclosure [Abstract]
Schedule of Finite-Lived Intangible Assets	The Company’s various intangible assets consisted of the following as of (amounts in thousands): September 30, 2018 December 31, 2017 Intangibles Gross Accumulated Net Gross Accumulated Net Customer lists $ 59,213 $ (38,377 ) $ 20,836 $ 60,420 $ (31,698 ) $ 28,722 Technology 49,926 (37,976 ) 11,950 72,204 (43,270 ) 28,934 Trademarks 7,447 (4,401 ) 3,046 7,680 (3,730 ) 3,950 Total finite lived intangibles 116,586 (80,754 ) 35,832 140,304 (78,698 ) 61,606 Trademark not subject to amortization (1) 363 — 363 363 — 363 Total intangibles $ 116,949 $ (80,754 ) $ 36,195 $ 140,667 $ (78,698 ) $ 61,969 (1) These indefinite-life trademarks relate to the forex.com and foreignexchange.com domain names where management determined there was no legal, regulatory or technological limitation on their useful lives. The Company compares the recorded value of the indefinite-life intangible assets to their fair value on an annual basis and whenever circumstances arise that indicate that impairment may have occurred. The Company had the following identifiable intangible assets and weighted average amortization periods as of September 30, 2018 : Intangible Assets Amount (in thousands) Weighted average amortization period Customer lists $ 59,213 7.4 years Technology 49,926 7.2 years Trademarks (1) 7,810 6.7 years Total intangible assets $ 116,949 (1) Trademarks with an indefinite-life, as described above, comprise $0.4 million of the $7.8 million of trademarks.
Schedule of Goodwill	The following represents the changes in the carrying amount of goodwill by segment (amounts in thousands): Retail Institutional Futures Total Carrying amount of goodwill as of December 31, 2017 $ 25,952 $ 4,650 $ 2,434 $ 33,036 Foreign currency translation adjustments (313 ) (34 ) (29 ) (376 ) Discontinued operations — (4,616 ) — (4,616 ) Carrying amount of goodwill as of September 30, 2018 $ 25,639 $ — $ 2,405 $ 28,044

OTHER ASSETS (Tables)

OTHER ASSETS (Tables)	9 Months Ended
	Sep. 30, 2018
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Schedule of Other Assets	Other assets consisted of the following as of (amounts in thousands): September 30, 2018 December 31, 2017 Vendor and security deposits $ 6,943 $ 11,923 Income tax receivable — 2,132 Deferred tax assets, net 12,563 10,698 GTX trade receivables 178 5,758 Customer debit positions 4,526 2,384 Allowance on customer debit positions (3,532 ) (1,959 ) Prepaid assets 11,490 9,523 Miscellaneous receivables 4,930 4,872 Deferred commitment fees 391 550 Total other assets $ 37,489 $ 45,881

NON-CONTROLLING INTERESTS (Tabl

NON-CONTROLLING INTERESTS (Tables)	9 Months Ended
	Sep. 30, 2018
Noncontrolling Interest [Abstract]
Summary of redeemable noncontrolling interest treatment	The table below reflects the non-controlling interests’ effects on the Company’s financial statements (amounts in thousands): Redeemable non-controlling interests January 1, 2018 $ 4,411 Adjustment to the redemption value of non-controlling interests 901 Net income attributable to non-controlling interests 638 Distributions to non-controlling interest holders (553 ) Purchase of additional shares of non-controlling interest (2,854 ) September 30, 2018 $ 2,543

CONVERTIBLE SENIOR NOTES (Table

CONVERTIBLE SENIOR NOTES (Tables)	9 Months Ended
	Sep. 30, 2018
Debt Disclosure [Abstract]
Schedule of Liability and Equity Components of Convertible Debt	The balances of the liability and equity components as of September 30, 2018 and December 31, 2017 were as follows (amounts in thousands): September 30, 2018 December 31, 2017 Liability component - principal $ 158,350 $ 158,350 Deferred bond discount (21,069 ) (25,624 ) Deferred financing cost (417 ) (505 ) Liability component - net carrying value $ 136,864 $ 132,221 Additional paid in capital $ 39,405 $ 39,405 Discount attributable to equity (826 ) (826 ) Equity component $ 38,579 $ 38,579
Schedule of Interest Expense	Interest expense related to the Convertible Senior Notes, included in Interest Expense on long term borrowings in the Condensed Consolidated Statements of Operations and Comprehensive Income , was as follows (amounts in thousands): For the Three Months Ended September 30, For the Nine Months Ended September 30, 2018 2017 2018 2017 Interest expense - stated coupon rate $ 1,834 $ 1,701 $ 5,503 $ 4,551 Interest expense - amortization of deferred bond discount and costs 1,570 1,284 4,629 3,793 Total interest expense - convertible senior notes $ 3,404 $ 2,985 $ 10,132 $ 8,344

EARNINGS_(LOSS) PER COMMON SH_2

EARNINGS/(LOSS) PER COMMON SHARE (Tables)	9 Months Ended
	Sep. 30, 2018
Earnings Per Share [Abstract]
Computation of Earnings Per Share	The following table sets forth the computation of earnings/(loss) 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, 2018 2017 2018 2017 Net income/(loss) from continuing operations $ 9,969 $ (3,080 ) $ 28,715 $ (8,026 ) Less income attributable to non-controlling interests $ 137 $ 225 $ 638 $ 463 Net income/(loss) from continuing operations $ 9,832 $ (3,305 ) $ 28,077 $ (8,489 ) Adjustment (1) (10 ) 728 (901 ) 1,711 Net income/(loss) available to GAIN common shareholders from continuing operations $ 9,822 $ (2,577 ) $ 27,176 $ (6,778 ) Net income from discontinued operations 2,344 725 67,330 977 Weighted average common shares outstanding: Basic weighted average common shares outstanding 44,553,903 46,323,038 44,787,875 47,295,843 Effect of dilutive securities: Stock options 238,172 206,964 258,934 247,575 RSUs/RSAs 192,646 — 223,988 4,615 Diluted weighted average common shares outstanding 44,984,721 46,323,038 45,270,797 47,295,843 Basic earnings/(loss) from continuing operations $ 0.22 $ (0.06 ) $ 0.61 $ (0.14 ) Basic earnings from discontinued operations $ 0.05 $ 0.02 $ 1.50 $ 0.02 Diluted earnings/(loss) from continuing operations $ 0.22 $ (0.06 ) $ 0.60 $ (0.14 ) Diluted earnings from discontinued operations $ 0.05 $ 0.02 $ 1.49 $ 0.02 (1) During the three and nine months ended September 30, 2018 and 2017 , the Company concluded that the carrying value of the Company's redeemable noncontrolling interests was less than their redemption value, requiring that an adjustment to the carrying value be recorded for purposes of calculating earnings/(loss) per common share. The adjustment to increase or reduce the carrying value will, respectively, reduce or increase earnings/(loss) per common share by reducing or increasing net income available to common shareholders.

REGULATORY REQUIREMENTS (Tables

REGULATORY REQUIREMENTS (Tables)	9 Months Ended
	Sep. 30, 2018
Banking and Thrift [Abstract]
Regulatory Capital Subsidiaries Required to Maintain	The following table illustrates the minimum regulatory capital our subsidiaries were required to maintain as of September 30, 2018 and the actual amounts of capital that were maintained (amounts in millions): Entity Name Minimum Capital Excess Percent of GAIN Capital Group, LLC $ 34.3 $ 51.9 $ 17.6 151 % GAIN Capital Securities, Inc. 0.1 0.4 0.3 400 % GAIN Capital U.K., Ltd. 69.1 198.5 129.4 287 % GAIN Capital Japan Co., Ltd. 1.4 9.7 8.3 693 % GAIN Capital Australia, Pty. Ltd. 0.7 5.7 5.0 814 % GAIN Capital-Forex.com Hong Kong, Ltd. 1.9 3.7 1.8 195 % GAIN Global Markets, Inc. 0.7 1.3 0.6 186 % GAIN Capital-Forex.com Canada, Ltd. 0.2 1.5 1.3 750 % GAIN Capital Singapore Pte., Ltd. 0.4 8.1 7.7 2,025 % Trade Facts, Ltd. 0.6 3.5 2.9 583 % Global Asset Advisors, LLC 0.0 2.2 2.2 100 % GTX SEF, LLC 0.7 0.9 0.2 129 % Total $ 110.1 $ 287.4 $ 177.3 261 %

SEGMENT INFORMATION (Tables)

SEGMENT INFORMATION (Tables)	9 Months Ended
	Sep. 30, 2018
Segment Reporting [Abstract]
Selected Financial Information by Segment	Selected financial information by segment is presented in the following tables (amounts in thousands): Retail Three Months Ended September 30, Nine Months Ended September 30, 2018 2017 2018 2017 Net revenue $ 85,856 $ 63,927 $ 246,060 $ 184,619 Employee compensation and benefits 14,355 12,726 43,427 40,466 Selling and marketing 9,957 6,280 22,117 22,429 Referral fees 5,321 9,796 20,047 31,945 Other operating expenses 17,194 15,634 53,206 44,253 Segment profit $ 39,029 $ 19,491 $ 107,263 $ 45,526 Futures Three Months Ended September 30, Nine Months Ended September 30, 2018 2017 2018 2017 Net revenue $ 9,737 $ 9,777 $ 33,328 $ 30,757 Employee compensation and benefits 2,416 2,327 7,790 7,372 Selling and marketing 181 121 625 607 Referral fees 2,827 3,128 9,996 10,732 Other operating expenses 3,043 2,904 10,392 9,879 Segment profit $ 1,270 $ 1,297 $ 4,525 $ 2,167 Corporate and Other Three Months Ended September 30, Nine Months Ended September 30, 2018 2017 2018 2017 Other revenue/(loss) $ (52 ) $ 56 $ (1,302 ) $ 155 Employee compensation and benefits 6,082 5,758 18,447 16,507 Selling and marketing 77 1 211 118 Other operating expenses 3,581 2,202 10,550 7,438 Loss $ (9,792 ) $ (7,905 ) $ (30,510 ) $ (23,908 )
Reconciliation of Operating Segment Profit to Income Before Income Tax Expense	Reconciliation of operating segment profit to Income before income tax expense Three Months Ended September 30, Nine Months Ended September 30, 2018 2017 2018 2017 Retail segment $ 39,029 $ 19,491 $ 107,263 $ 45,526 Futures segment 1,270 1,297 4,525 2,167 Corporate and other (9,792 ) (7,905 ) (30,510 ) (23,908 ) SEGMENT PROFIT 30,507 12,883 81,278 23,785 Depreciation and amortization 4,685 4,373 15,394 12,322 Purchased intangible amortization 3,504 3,524 10,784 10,407 Restructuring expenses — — 25 — Contingent provision 4,975 — 4,975 — Impairment of investment — — (130 ) — OPERATING PROFIT 17,343 4,986 50,230 1,056 Interest expense on long term borrowings 3,404 2,985 10,132 8,344 Loss on extinguishment of debt — 4,944 $ — $ 4,944 INCOME/(LOSS) BEFORE INCOME TAX EXPENSE $ 13,939 $ (2,943 ) $ 40,098 $ (12,232 )

DESCRIPTION OF BUSINESS AND B_3

DESCRIPTION OF BUSINESS AND BASIS OF PRESENTATION (Details) $ in Millions	9 Months Ended
	Sep. 30, 2018segment	Jun. 29, 2018USD ($)
Accounting Policies [Abstract]
Number of operating segments | segment	2
Discontinued Operations, Disposed of by Sale | GTX ECN
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Disposal group, including discontinued operation, consideration		$ 100
Working capital adjustment		$ 0.2

ACCOUNTING PRONOUNCEMENTS (Deta

ACCOUNTING PRONOUNCEMENTS (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net cash provided by operating activities of continuing operations	$ 23,802	$ (16,060)
Accounting Standards Update 2016-18
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net cash provided by operating activities of continuing operations		$ 18,500

DISCONTINUED OPERATIONS (Detail

DISCONTINUED OPERATIONS (Details) - USD ($) $ in Thousands	Jun. 29, 2018	Sep. 30, 2018	Jun. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
INCOME/(LOSS) BEFORE INCOME TAX EXPENSE/(BENEFIT)			$ 69,439
Income tax expense/(benefit)			$ 3,222
NET INCOME FROM DISCONTINUED OPERATIONS		$ 2,344		$ 725	$ 67,330	$ 977
GTX ECN | Discontinued Operations, Disposed of by Sale
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Disposal group, including discontinued operation, consideration	$ 100,000
Working capital adjustment	200
Gain on sale of discontinued operations	69,400	(142)		0	69,439	0
Total non-interest revenue		0		7,520	16,377	23,322
Interest revenue		0		33	103	81
Total net interest revenue		0		33	103	81
Net revenue		0		7,553	16,480	23,403
Employee compensation and benefits		94		2,993	5,973	9,999
Trading expenses		0		2,409	5,439	7,320
Other expenses		30		1,104	3,955	4,287
Total operating expense		124		6,506	15,367	21,606
OPERATING PROFIT/(LOSS)		(124)		1,047	1,113	1,797
Gain/(loss) on sale of discontinued operations	$ 69,400	(142)		0	69,439	0
INCOME/(LOSS) BEFORE INCOME TAX EXPENSE/(BENEFIT)		(266)		1,047	70,552	1,797
Income tax expense/(benefit)		(2,610)		322	3,222	820
NET INCOME FROM DISCONTINUED OPERATIONS		2,344		725	67,330	977
Total assets of discontinued operations							$ 28,500
Total liabilities of discontinued operations							$ 3,800
GTX ECN | Discontinued Operations, Disposed of by Sale | Institutional revenue
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Total non-interest revenue		0		7,520	16,379	23,322
GTX ECN | Discontinued Operations, Disposed of by Sale | Other revenue/(loss)
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Total non-interest revenue		$ 0		$ 0	$ (2)	$ 0

REVENUE RECOGNITION - Narrative

REVENUE RECOGNITION - Narrative (Details) $ in Millions	9 Months Ended
	Sep. 30, 2018USD ($)
Difference between Revenue Guidance in Effect before and after Topic 606 | Accounting Standards Update 2014-09
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue from contract with customer	$ 1

REVENUE RECOGNITION - Disaggreg

REVENUE RECOGNITION - Disaggregation of Revenue (Details) - Futures - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2018
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	$ 9,737	$ 33,328
Direct Customers
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	2,106	7,272
Indirect Customers
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	5,270	18,854
Other
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	$ 2,361	$ 7,202

FAIR VALUE MEASUREMENT - Assets

FAIR VALUE MEASUREMENT - Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - Recurring - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total	$ 485,025	$ 456,543
Money market accounts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	265,260	219,286
US treasury bills: U.S. government and agency securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	103,109	105,190
Broker derivative contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	(8,148)	4,966
Liabilities		3,170
Certificates of deposit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	176	175
Other
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	119	130
Customer derivative contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities	121,174	129,966
Broker derivative contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities	3,335
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total	368,664	324,781
Level 1 | Money market accounts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	265,260	219,286
Level 1 | US treasury bills: U.S. government and agency securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	103,109	105,190
Level 1 | Broker derivative contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	0	0
Level 1 | Certificates of deposit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	176	175
Level 1 | Other
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	119	130
Level 1 | Customer derivative contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities	0	0
Level 1 | Broker derivative contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities	0
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total	116,361	131,762
Level 2 | Money market accounts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	0	0
Level 2 | US treasury bills: U.S. government and agency securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	0	0
Level 2 | Broker derivative contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	(8,148)	4,966
Liabilities		3,170
Level 2 | Certificates of deposit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	0	0
Level 2 | Other
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	0	0
Level 2 | Customer derivative contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities	121,174	129,966
Level 2 | Broker derivative contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities	3,335
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total	0	0
Level 3 | Money market accounts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	0	0
Level 3 | US treasury bills: U.S. government and agency securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	0	0
Level 3 | Broker derivative contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	0	0
Level 3 | Certificates of deposit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	0	0
Level 3 | Other
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	0	0
Level 3 | Customer derivative contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities	0	$ 0
Level 3 | Broker derivative contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities	$ 0

FAIR VALUE MEASUREMENT - Carryi

FAIR VALUE MEASUREMENT - Carrying Value and Fair Value of Financial Assets and Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Financial Assets:
Receivables from brokers	$ 57,452	$ 78,503
Financial Liabilities:
Payables to brokers	1,754	2,789
Convertible senior notes	136,864	132,221
Derivative Assets | Level 1
Financial Assets:
Receivables from brokers	0	0
Financial Liabilities:
Payables to brokers		0
Derivative Assets | Level 2
Financial Assets:
Receivables from brokers	65,600	73,537
Financial Liabilities:
Payables to brokers		381
Derivative Assets | Level 3
Financial Assets:
Receivables from brokers	0	0
Financial Liabilities:
Payables to brokers		0
Derivative Assets | Carrying Value
Financial Assets:
Receivables from brokers	65,600	73,537
Financial Liabilities:
Payables to brokers		381
Derivative Assets | Fair Value
Financial Assets:
Receivables from brokers	65,600	73,537
Financial Liabilities:
Payables to brokers		381
Derivative Liabilities | Level 1
Financial Liabilities:
Payables to customers	0	0
Payables to brokers	0
Convertible senior notes	0	0
Derivative Liabilities | Level 2
Financial Liabilities:
Payables to customers	1,008,456	1,108,794
Payables to brokers	5,089
Convertible senior notes	164,501	205,073
Derivative Liabilities | Level 3
Financial Liabilities:
Payables to customers	0	0
Payables to brokers	0
Convertible senior notes	0	0
Derivative Liabilities | Carrying Value
Financial Liabilities:
Payables to customers	1,008,456	1,108,794
Payables to brokers	5,089
Convertible senior notes	136,864	132,221
Derivative Liabilities | Fair Value
Financial Liabilities:
Payables to customers	1,008,456	1,108,794
Payables to brokers	5,089
Convertible senior notes	$ 164,501	$ 205,073

DERIVATIVES - Fair Value of Der

DERIVATIVES - Fair Value of Derivative Instruments (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Derivatives, Fair Value [Line Items]
Gross amounts of assets for derivative open positions at fair value	$ 194,160	$ 227,847
Gross amount of (liabilities) for derivative open positions at fair value	(77,799)	(96,085)
Net amounts of assets/(liabilities) for derivative open positions at fair value	116,361	131,762
Receivables from brokers	57,452	78,503
Payables to customers	(887,282)	(978,828)
Payables to brokers	(1,754)	(2,789)
Receivables from brokers
Derivatives, Fair Value [Line Items]
Receivables from brokers	57,452	78,503
Receivables from brokers | Derivative Assets
Derivatives, Fair Value [Line Items]
Cash Collateral	65,600	73,537
Net amounts of assets/(liabilities) for derivative open positions at fair value	(8,148)	4,966
Payables to customers
Derivatives, Fair Value [Line Items]
Payables to customers	(887,282)	(978,828)
Payables to customers | Derivative Liabilities
Derivatives, Fair Value [Line Items]
Cash Collateral	1,008,456	1,108,794
Net amounts of assets/(liabilities) for derivative open positions at fair value	121,174	129,966
Foreign currency exchange contracts
Derivatives, Fair Value [Line Items]
Gross amounts of assets for derivative open positions at fair value	97,454	121,104
Gross amount of (liabilities) for derivative open positions at fair value	(21,747)	(31,556)
Net amounts of assets/(liabilities) for derivative open positions at fair value	75,707	89,548
CFD contracts
Derivatives, Fair Value [Line Items]
Gross amounts of assets for derivative open positions at fair value	88,122	102,659
Gross amount of (liabilities) for derivative open positions at fair value	(54,058)	(62,322)
Net amounts of assets/(liabilities) for derivative open positions at fair value	34,064	40,337
Metals contracts
Derivatives, Fair Value [Line Items]
Gross amounts of assets for derivative open positions at fair value	8,584	4,084
Gross amount of (liabilities) for derivative open positions at fair value	(1,994)	(2,207)
Net amounts of assets/(liabilities) for derivative open positions at fair value	6,590	1,877
Broker derivative contracts
Derivatives, Fair Value [Line Items]
Payables to brokers	(1,754)	(2,789)
Broker derivative contracts | Derivative Liabilities
Derivatives, Fair Value [Line Items]
Cash Collateral	(5,089)	381
Net amounts of assets/(liabilities) for derivative open positions at fair value	$ 3,335	$ (3,170)

DERIVATIVES - Notional Values o

DERIVATIVES - Notional Values of Derivative Instruments (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Total contracts in long positions
Derivative [Line Items]
Notional amounts of derivative	$ 2,432,615	$ 2,202,722
Total contracts in long positions | Foreign currency exchange contracts
Derivative [Line Items]
Notional amounts of derivative	2,323,419	2,075,789
Total contracts in long positions | CFD contracts
Derivative [Line Items]
Notional amounts of derivative	109,109	126,519
Total contracts in long positions | Metal contracts
Derivative [Line Items]
Notional amounts of derivative	87	414
Total contracts in short positions
Derivative [Line Items]
Notional amounts of derivative	3,183,274	4,323,108
Total contracts in short positions | Foreign currency exchange contracts
Derivative [Line Items]
Notional amounts of derivative	3,031,582	4,148,056
Total contracts in short positions | CFD contracts
Derivative [Line Items]
Notional amounts of derivative	151,645	174,835
Total contracts in short positions | Metal contracts
Derivative [Line Items]
Notional amounts of derivative	$ 47	$ 217

DERIVATIVES - Net Gains (Losses

DERIVATIVES - Net Gains (Losses) on Derivatives (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Derivative [Line Items]
Net gains (losses) on derivative instruments, total	$ 82,845	$ 62,143	$ 239,023	$ 180,147
Foreign currency exchange contracts
Derivative [Line Items]
Net gains (losses) on derivative instruments	57,619	30,487	150,484	91,496
CFD contracts
Derivative [Line Items]
Net gains (losses) on derivative instruments	16,298	25,073	68,126	78,286
Metal contracts
Derivative [Line Items]
Net gains (losses) on derivative instruments	$ 8,928	$ 6,583	$ 20,413	$ 10,365

RECEIVABLES FROM BROKERS (Detai

RECEIVABLES FROM BROKERS (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Receivables from Brokerage Clients [Line Items]
Receivables from brokers	$ 57,452	$ 78,503
Required collateral
Receivables from Brokerage Clients [Line Items]
Receivables from brokers	65,600	73,537
Open foreign exchange positions
Receivables from Brokerage Clients [Line Items]
Receivables from brokers	$ (8,148)	$ 4,966

PROPERTY AND EQUIPMENT - Schedu

PROPERTY AND EQUIPMENT - Schedule of Property and Equipment (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Gross property and equipment	$ 90,650	$ 93,236
Less: Accumulated depreciation and amortization	(57,193)	(52,494)
Property and equipment, net	33,457	40,742
Software
Property, Plant and Equipment [Line Items]
Gross property and equipment	59,442	57,047
Computer equipment
Property, Plant and Equipment [Line Items]
Gross property and equipment	13,744	18,390
Leasehold improvements
Property, Plant and Equipment [Line Items]
Gross property and equipment	10,904	11,068
Telephone equipment
Property, Plant and Equipment [Line Items]
Gross property and equipment	656	643
Office equipment
Property, Plant and Equipment [Line Items]
Gross property and equipment	1,945	2,110
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Gross property and equipment	3,324	3,592
Website development costs
Property, Plant and Equipment [Line Items]
Gross property and equipment	$ 635	$ 386

PROPERTY AND EQUIPMENT - Additi

PROPERTY AND EQUIPMENT - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Property, Plant and Equipment [Abstract]
Depreciation and amortization expense	$ 4,685	$ 4,373	$ 15,394	$ 12,322

INTANGIBLE ASSETS - Intangible

INTANGIBLE ASSETS - Intangible Assets (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Intangible Assets by Major Class [Line Items]
Finite-lived intangible assets, gross	$ 116,586		$ 116,586		$ 140,304
Accumulated Amortization	(80,754)		(80,754)		(78,698)
Finite-lived intangible assets, net	35,832		35,832		61,606
Total intangibles, gross	116,949		116,949		140,667
Intangible assets, net	36,195		36,195		61,969
Amortization of Intangible Assets	3,504	$ 3,524	10,784	$ 10,407
Payments to acquire intangible assets			0	$ 7,184
Forex Capital Markets L.L.C.
Intangible Assets by Major Class [Line Items]
Payments to acquire intangible assets					7,200
Trademarks
Intangible Assets by Major Class [Line Items]
Indefinite-lived intangible assets	363		363		363
Customer lists
Intangible Assets by Major Class [Line Items]
Finite-lived intangible assets, gross	59,213		59,213		60,420
Accumulated Amortization	(38,377)		(38,377)		(31,698)
Finite-lived intangible assets, net	20,836		20,836		$ 28,722
Total intangibles, gross	59,213		$ 59,213
Weighted average amortization period			7 years 4 months 12 days
Customer lists | Forex Capital Markets L.L.C.
Intangible Assets by Major Class [Line Items]
Weighted average amortization period					2 years
Technology
Intangible Assets by Major Class [Line Items]
Finite-lived intangible assets, gross	49,926		$ 49,926		$ 72,204
Accumulated Amortization	(37,976)		(37,976)		(43,270)
Finite-lived intangible assets, net	11,950		11,950		28,934
Total intangibles, gross	49,926		$ 49,926
Weighted average amortization period			7 years 2 months
Trademarks
Intangible Assets by Major Class [Line Items]
Finite-lived intangible assets, gross	7,447		$ 7,447		7,680
Accumulated Amortization	(4,401)		(4,401)		(3,730)
Finite-lived intangible assets, net	3,046		3,046		$ 3,950
Total intangibles, gross	$ 7,810		$ 7,810
Weighted average amortization period			6 years 8 months

INTANGIBLE ASSETS - Goodwill (D

INTANGIBLE ASSETS - Goodwill (Details)	9 Months Ended
	Sep. 30, 2018USD ($)reporting_unit
Goodwill [Line Items]
Number of reporting units | reporting_unit	2
Goodwill additions or impairments	$ 0
Goodwill	33,036,000
Decrease in goodwill	(5,000,000)
Goodwill [Roll Forward]
Goodwill. beginning balance	33,036,000
Foreign currency translation adjustments	(376,000)
Discontinued operations	(4,616,000)
Goodwill. ending balance	28,044,000
Operating Segments | Retail
Goodwill [Line Items]
Goodwill	25,952,000
Goodwill [Roll Forward]
Goodwill. beginning balance	25,952,000
Foreign currency translation adjustments	(313,000)
Discontinued operations	0
Goodwill. ending balance	25,639,000
Operating Segments | Institutional
Goodwill [Line Items]
Goodwill	4,650,000
Goodwill [Roll Forward]
Goodwill. beginning balance	4,650,000
Foreign currency translation adjustments	(34,000)
Discontinued operations	(4,616,000)
Goodwill. ending balance	0
Operating Segments | Futures
Goodwill [Line Items]
Goodwill	2,434,000
Goodwill [Roll Forward]
Goodwill. beginning balance	2,434,000
Foreign currency translation adjustments	(29,000)
Discontinued operations	0
Goodwill. ending balance	$ 2,405,000

OTHER ASSETS (Details)

OTHER ASSETS (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Vendor and security deposits	$ 6,943	$ 11,923
Income tax receivable	0	2,132
Deferred tax assets, net	12,563	10,698
GTX trade receivables	178	5,758
Customer debit positions	4,526	2,384
Allowance on customer debit positions	(3,532)	(1,959)
Prepaid assets	11,490	9,523
Miscellaneous receivables	4,930	4,872
Deferred commitment fees	391	550
Total other assets	$ 37,489	$ 45,881

RELATED PARTY TRANSACTIONS (Det

RELATED PARTY TRANSACTIONS (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Related Party Transaction [Line Items]
Payables to customers	$ 887,282	$ 978,828
Management
Related Party Transaction [Line Items]
Payables to customers	200	200
IPGL Limited
Related Party Transaction [Line Items]
Payables to customers	$ 12,400	$ 15,900

NON-CONTROLLING INTERESTS (Deta

NON-CONTROLLING INTERESTS (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Feb. 28, 2018	Dec. 31, 2016	Mar. 31, 2014
Redeemable Noncontrolling Interest [Line Items]
Purchase of minority ownership interests				$ 2,854	$ 0
Increase (Decrease) in Temporary Equity [Roll Forward]
Redeemable noncontrolling interest, beginning balance				4,411
Adjustment to the redemption value of non-controlling interests		$ 10	$ (728)	901	$ (1,711)
Net income attributable to non-controlling interests				638
Distributions to non-controlling interest holders				(553)
Purchase of additional shares of non-controlling interest				(2,854)
Redeemable noncontrolling interest, ending balance	$ 2,543	$ 2,543		$ 2,543
Global Asset Advisors, LLC
Redeemable Noncontrolling Interest [Line Items]
Purchase of minority ownership interests	$ 2,900
Global Asset Advisors, LLC
Redeemable Noncontrolling Interest [Line Items]
Percentage of company acquired (as percent)							24.00%	55.00%
Redeemable noncontrolling interest retained by noncontrolling owners (as percent)								45.00%
Noncontrolling interest by seller (as percent)						21.00%	21.00%
Top Third Ag Marketing, LLC
Redeemable Noncontrolling Interest [Line Items]
Percentage of company acquired (as percent)							24.00%	55.00%
Redeemable noncontrolling interest retained by noncontrolling owners (as percent)								45.00%
Noncontrolling interest by seller (as percent)							21.00%	45.00%

REVOLVING CREDIT ARRANGEMENT (D

REVOLVING CREDIT ARRANGEMENT (Details) - Revolving Credit Facility - USD ($)	Aug. 03, 2017	Sep. 30, 2018
Debt Instrument [Line Items]
Maximum amount under facility	$ 50,000,000
Commitment fee amount	400,000
Line of credit outstanding		$ 0
Maximum
Debt Instrument [Line Items]
Increase in borrowing capacity available	25,000,000
Minimum
Debt Instrument [Line Items]
Increase in borrowing capacity available	$ 5,000,000
Line of Credit
Debt Instrument [Line Items]
Term of credit facility	3 years

CONVERTIBLE SENIOR NOTES - Addi

CONVERTIBLE SENIOR NOTES - Additional Information (Details) - USD ($)	Aug. 22, 2017	Nov. 27, 2013	Sep. 30, 2018	Sep. 30, 2017	Mar. 31, 2016	Sep. 30, 2018	Sep. 30, 2017	Apr. 01, 2015
Debt Instrument [Line Items]
Proceeds from note offering						$ 0	$ 89,010,000
Repurchase of convertible notes						0	73,057,000
Loss on extinguishment of debt			$ 0	$ 4,944,000		$ 0	4,944,000
Convertible Notes Due 2022 | Convertible Debt
Debt Instrument [Line Items]
Principal amount	$ 92,000,000
Stated interest rate (as percent)	5.00%
Proceeds from note offering	$ 89,000,000
Convertible Notes Due 2020 | Convertible Debt
Debt Instrument [Line Items]
Principal amount								$ 60,000,000
Stated interest rate (as percent)								4.125%
Convertible Notes Due 2018 | Convertible Debt
Debt Instrument [Line Items]
Principal amount		$ 80,000,000		71,800,000	$ 1,900,000		$ 71,800,000
Stated interest rate (as percent)		4.125%
Proceeds from note offering		$ 77,900,000
Repurchase of convertible notes				73,700,000	$ 1,700,000
Loss on extinguishment of debt				$ 4,900,000

CONVERTIBLE SENIOR NOTES - Sche

CONVERTIBLE SENIOR NOTES - Schedule of Liability and Equity Components (Details) - Convertible Debt - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Liability component - principal	$ 158,350	$ 158,350
Deferred bond discount	(21,069)	(25,624)
Deferred financing cost	(417)	(505)
Liability component - net carrying value	136,864	132,221
Additional paid in capital	39,405	39,405
Discount attributable to equity	(826)	(826)
Equity component	$ 38,579	$ 38,579

CONVERTIBLE SENIOR NOTES - Sc_2

CONVERTIBLE SENIOR NOTES - Schedule of Interest Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Debt Instrument [Line Items]
Interest expense - amortization of deferred bond discount and costs			$ 489	$ 332
Convertible Debt
Debt Instrument [Line Items]
Interest expense - stated coupon rate	$ 1,834	$ 1,701	5,503	4,551
Interest expense - amortization of deferred bond discount and costs	1,570	1,284	4,629	3,793
Total interest expense - convertible senior notes	$ 3,404	$ 2,985	$ 10,132	$ 8,344

EARNINGS_(LOSS) PER COMMON SH_3

EARNINGS/(LOSS) PER COMMON SHARE - Additional Information (Detail) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive stock options excluded from calculation of diluted earnings per share	0.4	0.6	0.4	0.6
Common stock threshold for additional dilutive shares (in dollars per share)			$ 13
Convertible Notes Due 2018
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Dilutive securities, effect on basic earnings per share, dilutive convertible securities			$ 0
Convertible Notes Due 2020
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Dilutive securities, effect on basic earnings per share, dilutive convertible securities			1.5
Convertible Notes Due 2022
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Dilutive securities, effect on basic earnings per share, dilutive convertible securities			$ 4.2

EARNINGS_(LOSS) PER COMMON SH_4

EARNINGS/(LOSS) PER COMMON SHARE - Computation of Earnings Per Share (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Earnings Per Share [Abstract]
Net income/(loss) from continuing operations	$ 9,969	$ (3,080)	$ 28,715	$ (8,026)
Less income attributable to non-controlling interests	137	225	638	463
Net income/(loss) from continuing operations	9,832	(3,305)	28,077	(8,489)
Adjustment	(10)	728	(901)	1,711
Net income/(loss) available to GAIN common shareholders from continuing operations	9,822	(2,577)	27,176	(6,778)
Net income from discontinued operations	$ 2,344	$ 725	$ 67,330	$ 977
Weighted average common shares outstanding:
Basic weighted average common shares outstanding	44,553,903	46,323,038	44,787,875	47,295,843
Effect of dilutive securities:
Stock options (in shares)	238,172	206,964	258,934	247,575
RSUs/RSAs (in shares)	192,646	0	223,988	4,615
Diluted weighted average common shares outstanding	44,984,721	46,323,038	45,270,797	47,295,843
Earnings/(loss) per common share:
Basic earnings/(loss) from continuing operations (usd per share)	$ 0.22	$ (0.06)	$ 0.61	$ (0.14)
Basic earnings from discontinued operations (usd per share)	0.05	0.02	1.50	0.02
Diluted earnings/(loss) from continuing operations (usd per share)	0.22	(0.06)	0.60	(0.14)
Diluted earnings from discontinued operations (usd per share)	$ 0.05	$ 0.02	$ 1.49	$ 0.02

INCOME TAXES (Details)

INCOME TAXES (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Income Tax Disclosure [Abstract]
Provision (benefit) for income taxes	$ 3,970	$ 97	$ 11,383	$ (4,300)
Effective income tax rates (as percent)	28.50%	(3.30%)	28.40%	35.20%

REGULATORY REQUIREMENTS (Detail

REGULATORY REQUIREMENTS (Details) $ in Millions	Sep. 30, 2018USD ($)
Schedule Of Compliance With Regulatory Capital Requirements For Broker Dealer [Line Items]
Minimum Regulatory Capital Requirements	$ 110.1
Capital Levels Maintained	287.4
Excess Net Capital	$ 177.3
Percent of Requirement Maintained	261.00%
GAIN Capital Group, LLC
Schedule Of Compliance With Regulatory Capital Requirements For Broker Dealer [Line Items]
Minimum Regulatory Capital Requirements	$ 34.3
Capital Levels Maintained	51.9
Excess Net Capital	$ 17.6
Percent of Requirement Maintained	151.00%
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	0.4
Excess Net Capital	$ 0.3
Percent of Requirement Maintained	400.00%
GAIN Capital U.K., Ltd.
Schedule Of Compliance With Regulatory Capital Requirements For Broker Dealer [Line Items]
Minimum Regulatory Capital Requirements	$ 69.1
Capital Levels Maintained	198.5
Excess Net Capital	$ 129.4
Percent of Requirement Maintained	287.00%
GAIN Capital Japan Co., Ltd.
Schedule Of Compliance With Regulatory Capital Requirements For Broker Dealer [Line Items]
Minimum Regulatory Capital Requirements	$ 1.4
Capital Levels Maintained	9.7
Excess Net Capital	$ 8.3
Percent of Requirement Maintained	693.00%
GAIN Capital Australia, Pty. Ltd.
Schedule Of Compliance With Regulatory Capital Requirements For Broker Dealer [Line Items]
Minimum Regulatory Capital Requirements	$ 0.7
Capital Levels Maintained	5.7
Excess Net Capital	$ 5
Percent of Requirement Maintained	814.00%
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	3.7
Excess Net Capital	$ 1.8
Percent of Requirement Maintained	195.00%
GAIN Global Markets, Inc.
Schedule Of Compliance With Regulatory Capital Requirements For Broker Dealer [Line Items]
Minimum Regulatory Capital Requirements	$ 0.7
Capital Levels Maintained	1.3
Excess Net Capital	$ 0.6
Percent of Requirement Maintained	186.00%
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	1.5
Excess Net Capital	$ 1.3
Percent of Requirement Maintained	750.00%
GAIN Capital Singapore Pte., Ltd.
Schedule Of Compliance With Regulatory Capital Requirements For Broker Dealer [Line Items]
Minimum Regulatory Capital Requirements	$ 0.4
Capital Levels Maintained	8.1
Excess Net Capital	$ 7.7
Percent of Requirement Maintained	2025.00%
Trade Facts, Ltd.
Schedule Of Compliance With Regulatory Capital Requirements For Broker Dealer [Line Items]
Minimum Regulatory Capital Requirements	$ 0.6
Capital Levels Maintained	3.5
Excess Net Capital	$ 2.9
Percent of Requirement Maintained	583.00%
Global Asset Advisors, LLC
Schedule Of Compliance With Regulatory Capital Requirements For Broker Dealer [Line Items]
Minimum Regulatory Capital Requirements	$ 0
Capital Levels Maintained	2.2
Excess Net Capital	$ 2.2
Percent of Requirement Maintained	100.00%
GTX SEF, LLC
Schedule Of Compliance With Regulatory Capital Requirements For Broker Dealer [Line Items]
Minimum Regulatory Capital Requirements	$ 0.7
Capital Levels Maintained	0.9
Excess Net Capital	$ 0.2
Percent of Requirement Maintained	129.00%

SEGMENT INFORMATION - Additiona

SEGMENT INFORMATION - Additional Information (Details) $ in Millions	9 Months Ended
	Sep. 30, 2018market	Jun. 29, 2018USD ($)
Segment Reporting Information [Line Items]
Number of accessible global financial markets (more than) | market	12,500
GTX ECN | Discontinued Operations, Disposed of by Sale
Segment Reporting Information [Line Items]
Disposal group, including discontinued operation, consideration		$ 100
Working capital adjustment		$ 0.2

SEGMENT INFORMATION - Selected

SEGMENT INFORMATION - Selected Financial Information by Segment (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Employee compensation and benefits	$ 22,853	$ 20,811	$ 69,664	$ 64,345
Selling and marketing	10,215	6,402	22,953	23,154
Referral fees	8,148	12,924	30,043	42,677
Segment profit (loss)	30,507	12,883	81,278	23,785
Operating Segments | Retail
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Net revenue	85,856	63,927	246,060	184,619
Employee compensation and benefits	14,355	12,726	43,427	40,466
Selling and marketing	9,957	6,280	22,117	22,429
Referral fees	5,321	9,796	20,047	31,945
Other operating expenses	17,194	15,634	53,206	44,253
Segment profit (loss)	39,029	19,491	107,263	45,526
Operating Segments | Futures
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Net revenue	9,737	9,777	33,328	30,757
Employee compensation and benefits	2,416	2,327	7,790	7,372
Selling and marketing	181	121	625	607
Referral fees	2,827	3,128	9,996	10,732
Other operating expenses	3,043	2,904	10,392	9,879
Segment profit (loss)	1,270	1,297	4,525	2,167
Corporate and Other
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Net revenue	(52)	56	(1,302)	155
Employee compensation and benefits	6,082	5,758	18,447	16,507
Selling and marketing	77	1	211	118
Other operating expenses	3,581	2,202	10,550	7,438
Segment profit (loss)	$ (9,792)	$ (7,905)	$ (30,510)	$ (23,908)

SEGMENT INFORMATION - Reconcili

SEGMENT INFORMATION - Reconciliation of Operating Segment Profit to Income Before Income Tax Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
SEGMENT PROFIT	$ 30,507	$ 12,883	$ 81,278	$ 23,785
Depreciation and amortization	4,685	4,373	15,394	12,322
Purchased intangible amortization	3,504	3,524	10,784	10,407
Restructuring expenses	0	0	25	0
Contingent provision	4,975	0	4,975	0
Impairment of investment	0	0	(130)	0
OPERATING PROFIT	17,343	4,986	50,230	1,056
Interest expense on long term borrowings	3,404	2,985	10,132	8,344
INCOME/(LOSS) BEFORE INCOME TAX EXPENSE/(BENEFIT)	13,939	(2,943)	40,098	(12,232)
Operating Segments | Retail
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
SEGMENT PROFIT	39,029	19,491	107,263	45,526
Operating Segments | Futures
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
SEGMENT PROFIT	1,270	1,297	4,525	2,167
Corporate and Other
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
SEGMENT PROFIT	$ (9,792)	$ (7,905)	$ (30,510)	$ (23,908)

SUBSEQUENT EVENTS (Details)

SUBSEQUENT EVENTS (Details) - USD ($)	Oct. 25, 2018	Oct. 09, 2018	Sep. 30, 2018	Sep. 30, 2017
Subsequent Event [Line Items]
Common stock dividend declared (usd per share)			$ 0.06	$ 0.06
Subsequent event
Subsequent Event [Line Items]
Common stock dividend declared (usd per share)	$ 0.06
Modified Dutch Auction | Subsequent event
Subsequent Event [Line Items]
Tender offer to purchase shares		$ 50,000,000
Modified Dutch Auction | Subsequent event | Minimum
Subsequent Event [Line Items]
Share price (usd per share)		$ 7.24
Modified Dutch Auction | Subsequent event | Maximum
Subsequent Event [Line Items]
Share price (usd per share)		$ 7.94