GAIN Capital 10-Q8 Aug 172017 Q2 Quarterly reportFinancial data

Company Profile

Document and Entity Information

Document and Entity Information - shares	6 Months Ended
Document and Entity Information - shares	Jun. 30, 2017	Aug. 03, 2017
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
Document Type	10-Q
Document Period End Date	Jun. 30, 2017
Document Fiscal Year Focus	2,017
Document Fiscal Period Focus	Q2
Amendment Flag	false
Entity Common Stock, Shares Outstanding		47,241,825

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
ASSETS:
Cash and cash equivalents	$ 193,137	$ 234,760
Cash and securities held for customers	947,328	945,468
Receivables from brokers	80,671	61,096
Property and equipment, net	39,697	36,462
Intangible assets, net	68,661	67,358
Goodwill	32,652	32,107
Other assets	53,803	52,833
Total assets	1,415,949	1,430,084
Liabilities
Payables to customers	947,328	945,468
Accrued compensation and benefits	8,882	13,559
Accrued expenses and other liabilities	36,540	41,547
Income tax payable	400	3,965
Convertible senior notes	127,278	124,769
Total liabilities	1,120,428	1,129,308
Commitments and contingent liabilities
Redeemable non-controlling interests	4,976	6,594
Shareholders’ equity
Common stock ($0.00001 par value; 120 million shares authorized, 53,625,129 shares issued and 47,449,481 shares outstanding as of June 30, 2017; 120 million shares authorized, 52,848,811 shares issued and 48,220,243 shares outstanding as of December 31, 2016)	0	0
Additional paid-in capital	221,985	218,392
Retained earnings	133,676	143,399
Accumulated other comprehensive loss	(24,542)	(36,842)
Treasury stock, at cost (6,057,443 shares at June 30, 2017 and 4,628,568 at December 31, 2016)	(40,574)	(30,767)
Total shareholders’ equity	290,545	294,182
Total liabilities and shareholders’ equity	$ 1,415,949	$ 1,430,084

Condensed Consolidated Balance3

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Jun. 30, 2017	Dec. 31, 2016
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)	53,506,924	52,848,811
Common stock, shares outstanding (in shares)	47,449,481	48,220,243
Treasury stock, shares (in shares)	6,057,443	4,628,568

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations and Comprehensive Income/(Loss) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
REVENUE:
Retail revenue	$ 79,079,000	$ 88,083,000	$ 118,010,000	$ 183,125,000
Institutional revenue	7,435,000	7,209,000	15,802,000	13,916,000
Futures revenue	9,565,000	12,743,000	20,145,000	24,761,000
Other revenue	822,000	(60,000)	1,833,000	1,513,000
Total non-interest revenue	96,901,000	107,975,000	155,790,000	223,315,000
Interest revenue	1,289,000	443,000	2,130,000	761,000
Interest expense	136,000	128,000	299,000	232,000
Total net interest revenue	1,153,000	315,000	1,831,000	529,000
Net revenue	98,054,000	108,290,000	157,621,000	223,844,000
EXPENSES:
Employee compensation and benefits	26,325,000	26,615,000	50,540,000	53,008,000
Selling and marketing	7,527,000	6,805,000	16,783,000	13,244,000
Referral fees	13,312,000	17,553,000	29,753,000	38,216,000
Trading expenses	7,178,000	7,761,000	15,245,000	16,194,000
General and administrative	12,768,000	15,027,000	22,505,000	31,065,000
Depreciation and amortization	4,340,000	3,559,000	8,359,000	6,712,000
Purchased intangible amortization	4,354,000	3,843,000	7,956,000	7,765,000
Communications and technology	4,602,000	5,684,000	9,754,000	10,963,000
Bad debt provision	(166,000)	1,189,000	(94,000)	1,761,000
Restructuring expenses	0	22,000	0	803,000
Integration expenses	0	1,043,000	0	1,856,000
Legal settlement	0	0	0	9,412,000
Total operating expense	80,240,000	89,101,000	160,801,000	190,999,000
OPERATING PROFIT/(LOSS)	17,814,000	19,189,000	(3,180,000)	32,845,000
Interest expense on long term borrowings	2,694,000	2,560,000	5,359,000	5,152,000
INCOME/(LOSS) BEFORE INCOME TAX EXPENSE/(BENEFIT)	15,120,000	16,629,000	(8,539,000)	27,693,000
Income tax expense/(benefit)	994,000	5,025,000	(3,899,000)	7,372,000
Equity in net loss of affiliate	(34,000)	(18,000)	(54,000)	(34,000)
NET INCOME/(LOSS)	14,092,000	11,586,000	(4,694,000)	20,287,000
Net income attributable to non-controlling interests	153,000	745,000	238,000	1,094,000
NET INCOME/(LOSS) APPLICABLE TO GAIN CAPITAL HOLDINGS, INC.	13,939,000	10,841,000	(4,932,000)	19,193,000
Other comprehensive income/(loss):
Foreign currency translation adjustment	7,761,000	(10,249,000)	12,300,000	(12,993,000)
NET COMPREHENSIVE INCOME/(LOSS) APPLICABLE TO GAIN CAPITAL HOLDINGS, INC.	$ 21,700,000	$ 592,000	$ 7,368,000	$ 6,200,000
Earnings/(loss) per common share:
Basic (usd per share)	$ 0.31	$ 0.19	$ (0.08)	$ 0.36
Diluted (usd per share)	$ 0.31	$ 0.19	$ (0.08)	$ 0.36
Weighted average common shares outstanding used in computing earnings/(loss) per common share:
Basic (shares)	47,687,214	48,546,253	47,790,307	48,584,534
Diluted (shares)	47,894,648	48,737,188	47,790,307	48,860,533

Condensed Consolidated Stateme5

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, 2015		48,771,015
BEGINNING BALANCE at Dec. 31, 2015	$ 306,084	$ 0	$ (21,808)	$ 212,981	$ 120,776	$ (5,865)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss) applicable to Gain Capital Holdings, Inc.	19,193				19,193
Exercise of options (in shares)		150,566
Exercise of options	577			577
Employee stock purchase plan (in shares)		63,338
Employee stock purchase plan	400			400
Purchase of treasury stock (in shares)		(775,924)
Purchase of treasury stock	(5,384)		(5,384)
Shares withheld for net settlements of share-based awards (in shares)		(9,330)
Shares withheld for net settlements of share-based awards	(65)		(65)
Share-based compensation	2,148			2,148
Adjustment to fair value of redeemable non-controlling interests	(1,591)				(1,591)
Dividends declared	(4,837)				(4,837)
Foreign currency translation adjustment	(12,993)					(12,993)
Conversion of restricted stock into common stock (in shares)		434,699
Conversion of restricted stock into common stock	0
Tax benefit of stock options exercises	119			119
Convertible note buyback	(105)			(105)
ENDING BALANCE (in shares) at Jun. 30, 2016		48,634,364
ENDING BALANCE at Jun. 30, 2016	303,546	$ 0	(27,257)	216,120	133,541	(18,858)
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.	(4,932)				(4,932)
Exercise of options (in shares)		82,774
Exercise of options	335			335
Conversion of restricted stock into common stock (in shares)		510,793
Conversion of restricted stock into common stock	0
Employee stock purchase plan (in shares)		64,546
Employee stock purchase plan	402			402
Purchase of treasury stock (in shares)		(1,373,685)
Purchase of treasury stock	(9,426)		(9,426)
Shares withheld for net settlements of share-based awards (in shares)		(55,190)
Shares withheld for net settlements of share-based awards	(381)		(381)
Share-based compensation	2,856			2,856
Adjustment to fair value of redeemable non-controlling interests	983				983
Dividends declared	(5,774)				(5,774)
Foreign currency translation adjustment	12,300					12,300
ENDING BALANCE (in shares) at Jun. 30, 2017		47,449,481
ENDING BALANCE at Jun. 30, 2017	$ 290,545	$ 0	$ (40,574)	$ 221,985	$ 133,676	$ (24,542)

Condensed Consolidated Stateme6

Condensed Consolidated Statement of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016
CASH FLOWS FROM OPERATING ACTIVITIES:
Net (loss)/income	$ (4,694)	$ 20,287
Adjustments to reconcile net (loss)/income to cash (used in)/provided by operating activities
(Gain)/loss on foreign currency exchange rates	(97)	1,357
Depreciation and amortization	16,315	14,477
Non-cash integration costs	0	366
Deferred tax expense/(benefit)	622	(1,416)
Amortization of deferred financing costs	221	221
Bad debt provision	(94)	1,761
Convertible senior notes discount amortization	2,289	2,112
Share-based compensation	2,856	2,148
Gain on extinguishment of debt	0	(89)
Equity in net loss of affiliate	54	34
Changes in operating assets and liabilities:
Cash and securities held for customers	20,183	(161,579)
Receivables from brokers	(20,036)	(97,988)
Other assets	518	(5,503)
Payable to brokers, dealers, FCM's, Customers	(20,183)	166,784
Accrued compensation and benefits	(4,891)	(3,061)
Accrued expenses and other liabilities	(6,176)	1,303
Income tax payable	(2,699)	5,540
Net cash used in by operating activities	(15,812)	(53,246)
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchases of property and equipment	(10,182)	(12,185)
Acquisition of FXCM assets	(6,960)	0
Net cash used in investing activities	(17,142)	(12,185)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from exercise of stock options	335	577
Proceeds from employee stock purchase plan	402	400
Purchase of treasury stock	(9,807)	(5,449)
Excess tax benefit from employee stock option exercises	0	302
Dividend payments	(5,774)	(4,837)
Distributions to non-controlling interest holders	(873)	(525)
Repurchase of convertible notes	0	(1,735)
Net cash used in financing activities	(15,717)	(11,267)
Effect of exchange rate changes on cash and cash equivalents	7,048	(5,743)
NET DECREASE IN CASH AND CASH EQUIVALENTS	(41,623)	(82,441)
CASH AND CASH EQUIVALENTS—Beginning of period	234,760	171,888
CASH AND CASH EQUIVALENTS—End of period	193,137	89,447
Cash (paid)/received during the year for:
Interest	(3,148)	(3,081)
Income taxes	(4,386)	142
Non-cash financing activities:
Adjustment to redemption value of non-controlling interests	$ 983	$ (1,591)

DESCRIPTION OF BUSINESS AND BAS

DESCRIPTION OF BUSINESS AND BASIS OF PRESENTATION	6 Months Ended
DESCRIPTION OF BUSINESS AND BASIS OF PRESENTATION	Jun. 30, 2017
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. (previously known as "City Index (Holdings) Ltd" or "City Index") 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 three 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, spread bets and contracts for difference, or CFDs, on commodities, indices, individual equities, options and interest rate products, as well as OTC options on forex. The Company's institutional segment provides agency execution services and electronic access to spot and forward foreign exchange and precious metals markets via the electronic communications network, or ECN, GTX. The Company's futures segment offers execution and risk management services for exchange-traded futures and futures options on major U.S. and European futures and options exchanges. For more information about the Company's segments, please see Note 17. 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-Forex.com U.K. Ltd. (“GCUK1”) and GAIN Capital UK Limited ("GCUK2") are each registered in the United Kingdom ("U.K.") and regulated by the Financial Conduct Authority (“FCA”) as full scope €730k IFPRU Investment Firms. 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. 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, 2016. 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.

RECENT ACCOUNTING PRONOUNCEMENT

RECENT ACCOUNTING PRONOUNCEMENTS	6 Months Ended
RECENT ACCOUNTING PRONOUNCEMENTS	Jun. 30, 2017
Accounting Changes and Error Corrections [Abstract]
RECENT ACCOUNTING PRONOUNCEMENTS	RECENT ACCOUNTING PRONOUNCEMENTS 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 prospectively for the Company for the quarter ending December 31, 2020 , with early adoption permitted after January 1, 2017 . The impact of this guidance for the Company will depend on the outcomes of future goodwill impairment tests. In December 2016, the FASB issued technical corrections and improvements to revenue recognition guidance previously issued in May 2014 as discussed below. The FASB issued this update to address narrow aspects of the revenue recognition guidance issued in May 2014, which is not yet effective. The effective date and transition requirements for the amendments in this update are the same as the effective date and transition requirements of the revenue recognition guidance issued in May 2014. The Company is currently assessing the impact of adopting this guidance on its Condensed Consolidated Financial Statements. In November 2016, the FASB issued guidance requiring that amounts generally described as restricted cash and restricted cash equivalents be included with cash and cash equivalents when reconciling the beginning-of-period and end-of-period total amounts shown on the statement of cash flows. The guidance is effective for interim and annual periods beginning in 2018 and should be applied using a retrospective transition method to each period presented. Early adoption is permitted. The Company is currently evaluating the effect of the standard on its Condensed Consolidated Statement of Cash Flows. In August 2016, the FASB issued new guidance regarding the classification of certain cash receipts and cash payments on the Statements of Cash Flows. This new standard clarifies certain aspects of the statement of cash flows, including the classification of debt prepayment or debt extinguishment costs or other debt instruments with coupon interest rates that are insignificant in relation to the effective interest rate of the borrowing, contingent consideration payments made after a business combination, proceeds from the settlement of insurance claims, proceeds from the settlement of corporate-owned life insurance policies, distributions received from equity method investees and beneficial interests in securitization transactions. This new standard also clarifies that an entity should determine each separately identifiable source of use within the cash receipts and payments on the basis of the nature of the underlying cash flows. In situations in which cash receipts and payments have aspects of more than one class of cash flows and cannot be separated by source or use, the appropriate classification should depend on the activity that is likely to be the predominant source or use of cash flows for the item. The guidance is effective for fiscal years and interim periods within those fiscal years, beginning after December 15, 2017 . The Company is currently assessing the impact of adopting this guidance on its Condensed Consolidated Financial Statements. In May 2016, the FASB issued new guidance regarding the accounting for revenue from contracts with customers. The FASB issued this update to address certain issues related to assessing collectibility, presentation of sales taxes, non-cash consideration, completed contracts, and contract modifications at transition by reducing cost, complexity, and the potential for diversity in practice at initial application. The guidance affects the revenue recognition guidance issued in May 2014, which is not yet effective. The effective date and transition requirements for the amendments in this update are the same as the effective date and transition requirements of the revenue recognition guidance issued in May 2014, discussed below. The Company is currently assessing the impact of adopting this guidance on its Condensed Consolidated Financial Statements. In March and April 2016, the FASB issued new guidance regarding the accounting for revenue from contracts with customers. The FASB issued these updates to improve the operability and understandability of the implementation guidance on principal versus agent considerations, and to provide clarification on identifying performance obligations and the licensing implementation guidance, while retaining the related principles for those areas. The guidance affects the revenue recognition guidance issued in May 2014, which is not yet effective. The effective date and transition requirements for the amendments in this update are the same as the effective date and transition requirements of the revenue recognition guidance issued in May 2014, discussed below. The Company is currently assessing the impact of adopting this guidance on its Condensed Consolidated Financial Statements. In February 2016, the FASB issued new guidance regarding the accounting for leases. The FASB issued this update to increase transparency and comparability among organizations by 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. The Company is currently assessing the impact on its Condensed Consolidated Financial Statements of adopting this guidance. In May 2014, the FASB issued new revenue recognition guidance that supersedes the existing revenue recognition guidance and most industry-specific guidance applicable to revenue recognition. The guidance requires a company to recognize revenue when it transfers promised goods or services to customers. Recognition should be in an amount that reflects the consideration to which the company expects to be entitled in exchange for those services. The guidance requires enhanced disclosures to help users of financial statements better understand the nature, amount, timing, and uncertainty of revenues recognized. In July 2015, the FASB deferred the effective date of the new revenue recognition standard by one year, and it is effective for interim and annual periods beginning after December 15, 2017 . Early adoption is permitted, but no earlier than the original effective date of January 1, 2017 . The Company is currently assessing the impact of adopting this guidance on its Condensed Consolidated Financial Statements.

FAIR VALUE MEASUREMENT

FAIR VALUE MEASUREMENT	6 Months Ended
FAIR VALUE MEASUREMENT	Jun. 30, 2017
Fair Value Disclosures [Abstract]
FAIR VALUE MEASUREMENT	FAIR VALUE MEASUREMENT 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 $ 83,962 $ — $ — $ 83,962 Cash and securities held for customers: US treasury bills: U.S. government and agency securities 69,910 — — 69,910 Receivable from brokers: Broker derivative contracts — 1,394 — 1,394 Other assets: Certificates of deposit 175 — — 175 Other 125 — — 125 Payables to customers: Customer derivative contracts — 148,645 — 148,645 Total $ 154,172 $ 150,039 $ — $ 304,211 Fair Value Measurements on a Recurring Basis Level 1 Level 2 Level 3 Total Financial Assets (Liabilities): Cash and cash equivalents: Money market accounts $ 120,927 $ — $ — $ 120,927 Cash and securities held for customers: US treasury bills: U.S. government and agency securities 135,974 — — 135,974 Receivable from brokers: Broker derivative contracts — 5,228 — 5,228 Other assets: Certificates of deposit 175 — — 175 Other 115 — — 115 Payables to customers: Customer derivative contracts — 115,677 — 115,677 Total $ 257,191 $ 120,905 $ — $ 378,096 The Company has not changed its valuation techniques in measuring the fair value of any financial assets and liabilities during the six months ended June 30, 2017 , 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 securities 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. 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 June 30, 2017 or December 31, 2016 . 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 deposits, 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. The carrying value of Convertible senior notes represents the notes’ principal amounts net of unamortized discount (see Note 12). The Company assessed the notes' fair value as determined by current Company-specific and risk free interest rates as of the balance sheet date (amounts in thousands). As of June 30, 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 $ 79,277 $ 79,277 $ — $ 79,277 $ — Financial Liabilities: Payables to customers $ 1,095,973 $ 1,095,973 $ — $ 1,095,973 $ — Convertible senior notes $ 127,278 $ 124,568 $ — $ 124,568 $ — As of December 31, 2016 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 $ 55,868 $ 55,868 $ — $ 55,868 $ — Financial Liabilities: Payables to customers $ 1,061,146 $ 1,061,146 $ — $ 1,061,146 $ — Convertible senior notes $ 124,769 $ 122,544 $ — $ 122,544 $ —

DERIVATIVES

DERIVATIVES	6 Months Ended
DERIVATIVES	Jun. 30, 2017
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 and Payables to customers on the accompanying Condensed Consolidated Balance Sheets (amounts in thousands): June 30, 2017 Gross amounts of Gross amount of Net amounts of Derivative Instruments: Foreign currency exchange contracts $ 133,897 $ (36,428 ) $ 97,469 CFD contracts 84,198 (40,818 ) 43,380 Metals contracts 12,830 (3,640 ) 9,190 Total $ 230,925 $ (80,886 ) $ 150,039 June 30, 2017 Cash Collateral Net amounts of Net amounts of Derivative Assets/Liabilities: Receivables from brokers $ 79,277 $ 1,394 $ 80,671 Payables to customers $ (1,095,973 ) $ 148,645 $ (947,328 ) December 31, 2016 Gross amounts of Gross amount of Net amounts of Derivative Instruments: Foreign currency exchange contracts $ 130,301 $ (59,631 ) $ 70,670 CFD contracts 74,443 (37,241 ) 37,202 Metals contracts 18,766 (5,733 ) 13,033 Total $ 223,510 $ (102,605 ) $ 120,905 December 31, 2016 Cash Collateral Net amounts of Net amounts of Derivative Assets/Liabilities: Receivables from brokers $ 55,868 $ 5,228 $ 61,096 Payables to customers $ (1,061,145 ) $ 115,677 $ (945,468 ) 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 and Payables to customers on the Consolidated Balance Sheets are derived from the number of contracts below (amounts in thousands): June 30, 2017 Total contracts in long positions Total contracts in short positions Derivative Instruments: Foreign currency exchange contracts 2,848,711 4,613,766 CFD contracts 129,973 178,136 Metals contracts 1,094 409 Total 2,979,778 4,792,311 December 31, 2016 Total contracts in long positions Total contracts in short positions Derivative Instruments: Foreign currency exchange contracts 2,427,066 2,288,386 CFD contracts 112,685 156,308 Metals contracts 820 341 Total 2,540,571 2,445,035 The Company did not designate any of its derivatives as hedging instruments. Net gains with respect to derivative instruments are reflected in Retail revenue in the accompanying Condensed Consolidated Statements of Operations and Comprehensive Income/(Loss) for the three and six months ended June 30, 2017 and June 30, 2016 as follows (amounts in thousands): Three Months Ended June 30, Six Months Ended June 30, 2017 2016 2017 2016 Derivative Instruments: Foreign currency exchange contracts $ 43,633 $ 52,430 $ 61,009 $ 106,727 CFD contracts 26,422 29,659 53,213 64,881 Metals contracts 9,018 5,805 3,782 10,765 Total $ 79,073 $ 87,894 $ 118,004 $ 182,373

RECEIVABLES FROM BROKERS

RECEIVABLES FROM BROKERS	6 Months Ended
RECEIVABLES FROM BROKERS	Jun. 30, 2017
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): June 30, 2017 December 31, 2016 Required collateral $ 79,277 $ 55,868 Open foreign exchange positions 1,394 5,228 Total $ 80,671 $ 61,096

PROPERTY AND EQUIPMENT

PROPERTY AND EQUIPMENT	6 Months Ended
PROPERTY AND EQUIPMENT	Jun. 30, 2017
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): June 30, 2017 December 31, 2016 Software $ 63,143 $ 52,891 Computer equipment 21,453 19,797 Leasehold improvements 11,360 11,055 Telephone equipment 783 778 Office equipment 2,119 2,138 Furniture and fixtures 2,332 2,285 Web site development costs 644 644 Gross property and equipment 101,834 89,588 Less: Accumulated depreciation and amortization (62,137 ) (53,126 ) Property and equipment, net $ 39,697 $ 36,462 Depreciation and amortization expense for property and equipment was $4.3 million and $ 3.6 million for the three months ended June 30, 2017 and 2016 , respectively, and $8.4 million and $6.7 million for the six months ended June 30, 2017 and 2016 , respectively. The Company adjusted the amortization period of certain property and equipment that experienced changes in useful lives as a result of the City Index acquisition. This change in useful lives resulted in no additional charge during the three months ended June 30, 2017 and a charge of $0.2 million during the three months ended June 30, 2016 , respectively, and no additional charge during the six months ended June 30, 2017 and a charge of $0.4 million during the six months ended June 30, 2016 , respectively. The additional charge was recorded in Integration expenses .

INTANGIBLE ASSETS

INTANGIBLE ASSETS	6 Months Ended
INTANGIBLE ASSETS	Jun. 30, 2017
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): June 30, 2017 December 31, 2016 Intangibles Gross Accumulated Net Gross Accumulated Net Customer lists $ 59,105 $ (26,325 ) $ 32,780 $ 50,253 $ (20,928 ) $ 29,325 Technology 71,353 (40,160 ) 31,193 70,145 (37,074 ) 33,071 Trademarks 7,442 (3,117 ) 4,325 7,104 (2,505 ) 4,599 Total finite lived intangibles 137,900 (69,602 ) 68,298 127,502 (60,507 ) 66,995 Trademark not subject to amortization (1) 363 — 363 363 — 363 Total intangibles $ 138,263 $ (69,602 ) $ 68,661 $ 127,865 $ (60,507 ) $ 67,358 (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 June 30, 2017 : Intangible Assets Amount (in thousands) Weighted average amortization period Customer lists $ 59,105 6.9 years Technology 71,353 9.0 years Trademarks (1) 7,805 6.7 years Total intangible assets $ 138,263 (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 $4.4 million and $3.8 million for the three months ended June 30, 2017 and 2016 , respectively, and 8.0 million and $7.8 million for the six months ended June 30, 2017 and 2016 , 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 . In consideration of the transfer of these accounts, the Company agreed to pay FXCM, without duplication: • $500 per account for each transferred account that first executes a new trade with GAIN during the 76 -day period immediately following the closing of the account transfer (the "Initial Period"); and • $250 per account for each transferred account that (i) did not execute a new trade with GAIN during the Initial Period and (ii) executes a new trade with GAIN during the 77 -day period immediately following the last day of the Initial Period. The Company has paid $7.0 million to FXCM as consideration for the purchased accounts and has accrued an additional $0.1 million for the six months ended June 30, 2017 , which was capitalized and included as an intangible asset. Goodwill Goodwill is evaluated for impairment on an annual basis during the fourth quarter and in interim periods when events or changes indicate the carrying value may not be recoverable. The Company operates under three reporting units: retail, institutional and futures. There were no additions or impairments to the carrying value of the Company’s goodwill during the six months ended June 30, 2017 . As of June 30, 2017 and December 31, 2016 , the Company had recorded goodwill of approximately $32.7 million and $32.1 million , respectively. The increase was related to foreign currency translation adjustments. 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, 2016 $ 25,222 $ 4,519 $ 2,366 $ 32,107 Foreign currency translation adjustments 428 77 40 545 Carrying amount of goodwill as of June 30, 2017 $ 25,650 $ 4,596 $ 2,406 $ 32,652

OTHER ASSETS

OTHER ASSETS	6 Months Ended
OTHER ASSETS	Jun. 30, 2017
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
OTHER ASSETS	OTHER ASSETS Other assets consisted of the following as of (amounts in thousands): June 30, 2017 December 31, 2016 Vendor and security deposits $ 14,494 $ 9,670 Income tax receivable 4,565 1,017 Deferred tax assets, net 14,347 15,071 GTX trade receivables 4,232 7,515 Customer debit positions 8,505 9,781 Allowance on customer debit positions (8,338 ) (9,237 ) Insurance receivable 197 3,500 Prepaid assets 9,259 8,300 Miscellaneous receivables 5,963 6,615 Equity method investment 579 601 Total other assets $ 53,803 $ 52,833

RELATED PARTY TRANSACTIONS

RELATED PARTY TRANSACTIONS	6 Months Ended
RELATED PARTY TRANSACTIONS	Jun. 30, 2017
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 and $0.3 million at June 30, 2017 and December 31, 2016 , respectively. 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 Sheet. The aggregate amount of these funds was $13.3 million and $3.8 million as of June 30, 2017 and December 31, 2016 , respectively. The Company has certain receivables recorded in Other Assets due from certain officers of the Company related to taxes paid on equity exercises. The aggregate amount of these receivables was $0.6 million as of June 30, 2017 and was received on July 28, 2017. There were no receivables due from the Company's officers as of December 31, 2016 .

RESTRUCTURING

RESTRUCTURING	6 Months Ended
RESTRUCTURING	Jun. 30, 2017
Restructuring and Related Activities [Abstract]
RESTRUCTURING	RESTRUCTURING During 2016, the Company incurred restructuring expenses related to the global headcount reductions following the City Index acquisition. The Company incurred $0.8 million of restructuring expenses for the six months ended June 30, 2016 . These expenses are recorded in Restructuring expenses in the Condensed Consolidated Statements of Operations and Comprehensive Income/(Loss) . The restructuring liabilities have all been paid as of June 30, 2017 . The Company incurred no additional restructuring expenses for the six months ended June 30, 2017 .

NON-CONTROLLING INTERESTS

NON-CONTROLLING INTERESTS	6 Months Ended
NON-CONTROLLING INTERESTS	Jun. 30, 2017
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 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 interests' carrying value is determined by the Company's purchase prices and the non-controlling interests' share of the Company's subsequent net income (loss). 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, 2017 $ 6,594 Adjustment to the redemption value of non-controlling interests (983 ) Net income attributable to non-controlling interests 238 Distributions to non-controlling interest holders (873 ) June 30, 2017 $ 4,976

CONVERTIBLE SENIOR NOTES

CONVERTIBLE SENIOR NOTES	6 Months Ended
CONVERTIBLE SENIOR NOTES	Jun. 30, 2017
Debt Disclosure [Abstract]
CONVERTIBLE SENIOR NOTES	CONVERTIBLE SENIOR NOTES 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 . Convertible Senior Notes due 2018 On November 27 , 2013 , the Company issued $80.0 million aggregate principal amount of 4.125% Convertible Senior Notes maturing on 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 in 2018, for an aggregate purchase price of $1.7 million . Under accounting guidance, an entity must separately account for the liability and equity components of convertible debt instruments 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 of the Convertible Senior Notes as of June 30, 2017 and December 31, 2016 were as follows (amounts in thousands): June 30, 2017 December 31, 2016 Liability component - principal $ 138,150 $ 138,150 Deferred bond discount (10,748 ) (13,213 ) Deferred financing cost (124 ) (168 ) Liability component - net carrying value $ 127,278 $ 124,769 Additional paid in capital $ 27,822 $ 27,822 Discount attributable to equity (419 ) (419 ) Equity component $ 27,403 $ 27,403 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/(Loss) was as follows (amounts in thousands): For the Three Months Ended June 30, For the Six Months Ended June 30, 2017 2016 2017 2016 Interest expense - stated coupon rate $ 1,425 $ 1,431 $ 2,850 $ 2,875 Interest expense - amortization of deferred bond discount and costs 1,269 1,091 2,509 2,156 Total interest expense - convertible senior notes $ 2,694 $ 2,522 $ 5,359 $ 5,031

EARNINGS_(LOSS) PER COMMON SHAR

EARNINGS/(LOSS) PER COMMON SHARE	6 Months Ended
EARNINGS/(LOSS) PER COMMON SHARE	Jun. 30, 2017
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 0.2 million and 0.3 million stock options were excluded from the calculation of diluted earnings (loss) per share for the three and six months ended June 30, 2017 , respectively, as they were anti-dilutive. Approximately 0.3 million and 0.7 million stock options were excluded from the calculation of diluted earnings per share for the three and six months ended June 30, 2016 , 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 12. 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 both 2018 and 2020 convertible senior notes were satisfied, there would be an additional 0.5 million and 1.5 million dilutive shares as of June 30, 2017 , for the 2018 and 2020 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 June 30, For the Six Months Ended June 30, 2017 2016 2017 2016 Net income/(loss) applicable to GAIN Capital Holdings, Inc. $ 13,939 $ 10,841 $ (4,932 ) $ 19,193 Adjustment (1) 915 (1,690 ) 983 (1,591 ) Net income/(loss) available to GAIN common shareholders $ 14,854 $ 9,151 $ (3,949 ) $ 17,602 Weighted average common shares outstanding: Basic weighted average common shares outstanding 47,687,214 48,546,253 47,790,307 48,584,534 Effect of dilutive securities: Stock options 207,434 85,115 267,880 128,654 RSUs/RSAs — 105,820 6,923 147,345 Diluted weighted average common shares outstanding 47,894,648 48,737,188 47,790,307 48,860,533 Earnings/(loss) per common share: Basic $ 0.31 $ 0.19 $ (0.08 ) $ 0.36 Diluted $ 0.31 $ 0.19 $ (0.08 ) $ 0.36 (1) During the three and six months ended June 30, 2017 and 2016 , 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.

LEGAL

LEGAL	6 Months Ended
LEGAL	Jun. 30, 2017
Commitments and Contingencies Disclosure [Abstract]
LEGAL	LEGAL From time to time the Company becomes involved in legal proceedings and in each case the Company assesses the likely liability and/or the amount of damages as appropriate. Where available information indicates that it is probable a liability had been incurred at the date of the Condensed Consolidated Financial Statements and the Company can reasonably estimate the amount of that loss, the Company accrues the estimated loss by a charge to income. In many proceedings, however, it is inherently difficult to determine whether any loss is probable or even 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. Litigation On February 16, 2012, the Company received a Letter of Claim on behalf of certain individuals who had lost money in an investment scheme operated by a third-party money management firm, incorporated in the United Kingdom, which has since been closed down by the United Kingdom’s Financial Services Authority. The investment firm, Cameron Farley Ltd, had opened a corporate account with the Company and invested the individuals’ money, representing such funds as its own, while operating a fraudulent scheme. Though a complaint had been filed and served on the Company, the claimants requested, and the Company agreed, to follow the United Kingdom’s Pre-Action Protocol, a pre-litigation process intended to resolve matters without the need to engage in formal litigation. On April 28, 2016, the parties entered into a Settlement Agreement in which the Company agreed to make a one-time settlement payment in exchange for a full and final settlement of all claims. For the year ended December 31, 2016, the settlement amount, net of insurance recoveries, totaled approximately $9.2 million .

INCOME TAXES

INCOME TAXES	6 Months Ended
INCOME TAXES	Jun. 30, 2017
Income Tax Disclosure [Abstract]
INCOME TAXES	INCOME TAXES The Company's provision ( benefit ) for income taxes was approximately $1.0 million and $(3.9) million for the three and six months ended June 30, 2017 , respectively. The Company's provision for income taxes was approximately $5.0 million and $7.4 million for the three and six months ended June 30, 2016 , respectively. These amounts reflect the Company's estimate of the annual effective tax rates of 6.6% and 30.2% , adjusted for certain discrete items, for the three months ended June 30, 2017 and 2016 , respectively. The Company's effective tax rates of 45.7% and 26.6% for the six months ended June 30, 2017 and 2016 , respectively, reflect the Company's estimate of the annual effective tax rate adjusted for certain discrete items, primarily changes in uncertain tax positions. 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	6 Months Ended
REGULATORY REQUIREMENTS	Jun. 30, 2017
Banking and Thrift [Abstract]
REGULATORY REQUIREMENTS	REGULATORY REQUIREMENTS The following table illustrates the minimum regulatory capital our subsidiaries were required to maintain as of June 30, 2017 and the actual amounts of capital that were maintained (amounts in millions): Entity Name Minimum Capital Excess Percent of GAIN Capital Group, LLC $ 35.2 $ 45.5 $ 10.3 129 % GAIN Capital Securities, Inc. 0.1 0.4 0.3 400 % Trade Facts, Ltd. 0.6 3.1 2.5 517 % GAIN Capital-Forex.com Hong Kong, Ltd. 1.9 4.5 2.6 237 % GAIN Capital Australia Pty Ltd. 0.8 8.4 7.6 1,050 % GAIN Capital-Forex.com Canada Ltd. 0.2 1.3 1.1 650 % GAIN Capital-Forex.com U.K., Ltd. 5.1 16.7 11.6 327 % GAIN Capital Japan Co., Ltd. 1.3 8.9 7.6 685 % GAIN Global Markets, Inc. 0.8 1.4 0.6 175 % GAIN Capital UK, Ltd. 91.4 191.7 100.3 210 % GAIN Capital Singapore Pte, Ltd. 0.4 10.9 10.5 2,725 % Global Assets Advisors, LLC 0.1 1.4 1.3 1,400 % GAIN Capital Payments Ltd. 0.1 0.6 0.5 600 % Total $ 138.0 $ 294.8 $ 156.8 214 %

SEGMENT INFORMATION

SEGMENT INFORMATION	6 Months Ended
SEGMENT INFORMATION	Jun. 30, 2017
Segment Reporting [Abstract]
SEGMENT INFORMATION	SEGMENT INFORMATION The Company's segment reporting structure includes three operating segments: retail, institutional and futures. These operating segments are discussed in more detail below. The Company also reports information relating to general corporate services in a fourth component, corporate and other. Information in these Condensed Consolidated Financial Statements reflects the information presented to the chief operating decision maker. The chief operating decision maker does not review total assets by operating segment. 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 a diverse range of 12,500 global financial markets, including spot forex, precious metals, spread bets and CFDs on commodities, indices, individual equities, options 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. Institutional Segment The institutional segment provides agency execution services and offers access to markets in foreign exchange, commodities, equities, options and futures via an electronic communications network, or ECN, through the Company's GTX platform. We provide deep liquidity in spot and forward foreign exchange and precious metals to buy-side and sell-side firms, including banks, brokers, hedge funds, Commodity Trading Advisors and asset managers. The Company also offers high touch sales and trading aided by a team of sales employees. Futures Segment The futures segment offers execution and related services for exchange-traded futures and futures options on major U.S. and European exchanges. The Company offers futures services through its subsidiary, GAIN Capital Group, LLC, under the GAIN Capital Futures brand. 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 and also includes eliminations between operating segments which were $0.6 million and $0.3 million for the three months ended June 30, 2017 and 2016 , respectively, and $1.1 million and $0.7 million for the six months ended June 30, 2017 and 2016 , respectively. 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 June 30, Six Months Ended June 30, 2017 2016 2017 2016 Net revenue $ 80,605 $ 89,370 $ 120,691 $ 186,075 Employee compensation and benefits 16,630 16,897 31,978 33,599 Selling and marketing 7,244 6,546 16,149 12,760 Referral fees 9,826 13,699 22,149 30,301 Other operating expenses 15,978 20,749 30,460 41,628 Segment profit $ 30,927 $ 31,479 $ 19,955 $ 67,787 Institutional Three Months Ended June 30, Six Months Ended June 30, 2017 2016 2017 2016 Net revenue $ 7,690 $ 7,482 $ 16,311 $ 14,601 Employee compensation and benefits 3,588 3,462 7,630 6,664 Selling and marketing 10 35 31 41 Other operating expenses 2,928 2,518 6,155 4,959 Segment profit $ 1,164 $ 1,467 $ 2,495 $ 2,937 Futures Three Months Ended June 30, Six Months Ended June 30, 2017 2016 2017 2016 Net revenue $ 10,013 $ 12,857 $ 20,980 $ 25,060 Employee compensation and benefits 2,494 3,111 5,045 6,097 Selling and marketing 221 224 486 443 Referral fees 3,486 3,854 7,604 7,915 Other operating expenses 3,233 3,846 6,975 7,829 Segment profit $ 579 $ 1,822 $ 870 $ 2,776 Corporate and Other Three Months Ended June 30, Six Months Ended June 30, 2017 2016 2017 2016 Other revenue $ (254 ) $ (1,420 ) $ (362 ) $ (1,894 ) Employee compensation and benefits 3,964 3,145 6,489 6,648 Selling and marketing 52 — 116 — Other operating expenses 1,892 2,547 3,218 5,565 Loss $ (6,162 ) $ (7,112 ) $ (10,185 ) $ (14,107 ) Reconciliation of operating segment profit to Income before income tax expense Three Months Ended June 30, Six Months Ended June 30, 2017 2016 2017 2016 Retail segment $ 30,927 $ 31,479 $ 19,955 $ 67,787 Institutional segment 1,164 1,467 2,495 2,937 Futures segment 579 1,822 870 2,776 Corporate and other (6,162 ) (7,112 ) (10,185 ) (14,107 ) SEGMENT PROFIT 26,508 27,656 13,135 59,393 Depreciation and amortization 4,340 3,559 8,359 6,712 Purchased intangible amortization 4,354 3,843 7,956 7,765 Restructuring expenses — 22 — 803 Integration expenses — 1,043 — 1,856 Legal settlement — — — 9,412 OPERATING PROFIT/(LOSS) 17,814 19,189 (3,180 ) 32,845 Interest expense on long term borrowings 2,694 2,560 5,359 5,152 INCOME/(LOSS) BEFORE INCOME TAX EXPENSE $ 15,120 $ 16,629 $ (8,539 ) $ 27,693

SUBSEQUENT EVENTS

SUBSEQUENT EVENTS	6 Months Ended
SUBSEQUENT EVENTS	Jun. 30, 2017
Subsequent Events [Abstract]
SUBSEQUENT EVENTS	SUBSEQUENT EVENTS In August 2017, the Company announced the payment of a $0.06 dividend per share of Common Stock payable on September 19, 2017 to stockholders of record on September 12, 2017 . On August 3, 2017, GAIN Capital Holdings (the "Borrower”), Inc. entered into a Credit Agreement, dated as of August 2, 2017 , with Barclays Bank PLC , as Administrative Agent, Collateral Agent, Arranger and Documentation Agent, Sterling National Bank as Joint Bookrunner, and the other lenders from time to time party thereto. The Credit Agreement provides for a U.S $50 million senior secured first lien revolving credit facility (the "Facility”). Upon request of the Borrower, the Facility may be increased by up to $25 million , with a minimum increase of $5 million . Each Lender has the absolute discretion to provide all or any part of the requested increase, or to decline to participate in the increase.

DESCRIPTION OF BUSINESS AND B25

DESCRIPTION OF BUSINESS AND BASIS OF PRESENTATION (Policies)	6 Months Ended
	Jun. 30, 2017
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. 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, 2016. 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.
Recent Accounting Pronouncements	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 prospectively for the Company for the quarter ending December 31, 2020 , with early adoption permitted after January 1, 2017 . The impact of this guidance for the Company will depend on the outcomes of future goodwill impairment tests. In December 2016, the FASB issued technical corrections and improvements to revenue recognition guidance previously issued in May 2014 as discussed below. The FASB issued this update to address narrow aspects of the revenue recognition guidance issued in May 2014, which is not yet effective. The effective date and transition requirements for the amendments in this update are the same as the effective date and transition requirements of the revenue recognition guidance issued in May 2014. The Company is currently assessing the impact of adopting this guidance on its Condensed Consolidated Financial Statements. In November 2016, the FASB issued guidance requiring that amounts generally described as restricted cash and restricted cash equivalents be included with cash and cash equivalents when reconciling the beginning-of-period and end-of-period total amounts shown on the statement of cash flows. The guidance is effective for interim and annual periods beginning in 2018 and should be applied using a retrospective transition method to each period presented. Early adoption is permitted. The Company is currently evaluating the effect of the standard on its Condensed Consolidated Statement of Cash Flows. In August 2016, the FASB issued new guidance regarding the classification of certain cash receipts and cash payments on the Statements of Cash Flows. This new standard clarifies certain aspects of the statement of cash flows, including the classification of debt prepayment or debt extinguishment costs or other debt instruments with coupon interest rates that are insignificant in relation to the effective interest rate of the borrowing, contingent consideration payments made after a business combination, proceeds from the settlement of insurance claims, proceeds from the settlement of corporate-owned life insurance policies, distributions received from equity method investees and beneficial interests in securitization transactions. This new standard also clarifies that an entity should determine each separately identifiable source of use within the cash receipts and payments on the basis of the nature of the underlying cash flows. In situations in which cash receipts and payments have aspects of more than one class of cash flows and cannot be separated by source or use, the appropriate classification should depend on the activity that is likely to be the predominant source or use of cash flows for the item. The guidance is effective for fiscal years and interim periods within those fiscal years, beginning after December 15, 2017 . The Company is currently assessing the impact of adopting this guidance on its Condensed Consolidated Financial Statements. In May 2016, the FASB issued new guidance regarding the accounting for revenue from contracts with customers. The FASB issued this update to address certain issues related to assessing collectibility, presentation of sales taxes, non-cash consideration, completed contracts, and contract modifications at transition by reducing cost, complexity, and the potential for diversity in practice at initial application. The guidance affects the revenue recognition guidance issued in May 2014, which is not yet effective. The effective date and transition requirements for the amendments in this update are the same as the effective date and transition requirements of the revenue recognition guidance issued in May 2014, discussed below. The Company is currently assessing the impact of adopting this guidance on its Condensed Consolidated Financial Statements. In March and April 2016, the FASB issued new guidance regarding the accounting for revenue from contracts with customers. The FASB issued these updates to improve the operability and understandability of the implementation guidance on principal versus agent considerations, and to provide clarification on identifying performance obligations and the licensing implementation guidance, while retaining the related principles for those areas. The guidance affects the revenue recognition guidance issued in May 2014, which is not yet effective. The effective date and transition requirements for the amendments in this update are the same as the effective date and transition requirements of the revenue recognition guidance issued in May 2014, discussed below. The Company is currently assessing the impact of adopting this guidance on its Condensed Consolidated Financial Statements. In February 2016, the FASB issued new guidance regarding the accounting for leases. The FASB issued this update to increase transparency and comparability among organizations by 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. The Company is currently assessing the impact on its Condensed Consolidated Financial Statements of adopting this guidance. In May 2014, the FASB issued new revenue recognition guidance that supersedes the existing revenue recognition guidance and most industry-specific guidance applicable to revenue recognition. The guidance requires a company to recognize revenue when it transfers promised goods or services to customers. Recognition should be in an amount that reflects the consideration to which the company expects to be entitled in exchange for those services. The guidance requires enhanced disclosures to help users of financial statements better understand the nature, amount, timing, and uncertainty of revenues recognized. In July 2015, the FASB deferred the effective date of the new revenue recognition standard by one year, and it is effective for interim and annual periods beginning after December 15, 2017 . Early adoption is permitted, but no earlier than the original effective date of January 1, 2017 . The Company is currently assessing the impact of adopting this guidance on its Condensed Consolidated Financial Statements.

FAIR VALUE MEASUREMENT (Tables)

FAIR VALUE MEASUREMENT (Tables)	6 Months Ended
FAIR VALUE MEASUREMENT (Tables)	Jun. 30, 2017
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 $ 83,962 $ — $ — $ 83,962 Cash and securities held for customers: US treasury bills: U.S. government and agency securities 69,910 — — 69,910 Receivable from brokers: Broker derivative contracts — 1,394 — 1,394 Other assets: Certificates of deposit 175 — — 175 Other 125 — — 125 Payables to customers: Customer derivative contracts — 148,645 — 148,645 Total $ 154,172 $ 150,039 $ — $ 304,211 Fair Value Measurements on a Recurring Basis Level 1 Level 2 Level 3 Total Financial Assets (Liabilities): Cash and cash equivalents: Money market accounts $ 120,927 $ — $ — $ 120,927 Cash and securities held for customers: US treasury bills: U.S. government and agency securities 135,974 — — 135,974 Receivable from brokers: Broker derivative contracts — 5,228 — 5,228 Other assets: Certificates of deposit 175 — — 175 Other 115 — — 115 Payables to customers: Customer derivative contracts — 115,677 — 115,677 Total $ 257,191 $ 120,905 $ — $ 378,096
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 Company assessed the notes' fair value as determined by current Company-specific and risk free interest rates as of the balance sheet date (amounts in thousands). As of June 30, 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 $ 79,277 $ 79,277 $ — $ 79,277 $ — Financial Liabilities: Payables to customers $ 1,095,973 $ 1,095,973 $ — $ 1,095,973 $ — Convertible senior notes $ 127,278 $ 124,568 $ — $ 124,568 $ — As of December 31, 2016 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 $ 55,868 $ 55,868 $ — $ 55,868 $ — Financial Liabilities: Payables to customers $ 1,061,146 $ 1,061,146 $ — $ 1,061,146 $ — Convertible senior notes $ 124,769 $ 122,544 $ — $ 122,544 $ —

DERIVATIVES (Tables)

DERIVATIVES (Tables)	6 Months Ended
DERIVATIVES (Tables)	Jun. 30, 2017
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 and Payables to customers on the accompanying Condensed Consolidated Balance Sheets (amounts in thousands): June 30, 2017 Gross amounts of Gross amount of Net amounts of Derivative Instruments: Foreign currency exchange contracts $ 133,897 $ (36,428 ) $ 97,469 CFD contracts 84,198 (40,818 ) 43,380 Metals contracts 12,830 (3,640 ) 9,190 Total $ 230,925 $ (80,886 ) $ 150,039 June 30, 2017 Cash Collateral Net amounts of Net amounts of Derivative Assets/Liabilities: Receivables from brokers $ 79,277 $ 1,394 $ 80,671 Payables to customers $ (1,095,973 ) $ 148,645 $ (947,328 ) December 31, 2016 Gross amounts of Gross amount of Net amounts of Derivative Instruments: Foreign currency exchange contracts $ 130,301 $ (59,631 ) $ 70,670 CFD contracts 74,443 (37,241 ) 37,202 Metals contracts 18,766 (5,733 ) 13,033 Total $ 223,510 $ (102,605 ) $ 120,905 December 31, 2016 Cash Collateral Net amounts of Net amounts of Derivative Assets/Liabilities: Receivables from brokers $ 55,868 $ 5,228 $ 61,096 Payables to customers $ (1,061,145 ) $ 115,677 $ (945,468 )
Notional Values of Derivative Instruments	The amounts reported within Receivables from brokers and Payables to customers on the Consolidated Balance Sheets are derived from the number of contracts below (amounts in thousands): June 30, 2017 Total contracts in long positions Total contracts in short positions Derivative Instruments: Foreign currency exchange contracts 2,848,711 4,613,766 CFD contracts 129,973 178,136 Metals contracts 1,094 409 Total 2,979,778 4,792,311 December 31, 2016 Total contracts in long positions Total contracts in short positions Derivative Instruments: Foreign currency exchange contracts 2,427,066 2,288,386 CFD contracts 112,685 156,308 Metals contracts 820 341 Total 2,540,571 2,445,035
Net Gains (Losses) With Respect to Derivative Instruments Which are Reflected in Trading Revenue	Net gains with respect to derivative instruments are reflected in Retail revenue in the accompanying Condensed Consolidated Statements of Operations and Comprehensive Income/(Loss) for the three and six months ended June 30, 2017 and June 30, 2016 as follows (amounts in thousands): Three Months Ended June 30, Six Months Ended June 30, 2017 2016 2017 2016 Derivative Instruments: Foreign currency exchange contracts $ 43,633 $ 52,430 $ 61,009 $ 106,727 CFD contracts 26,422 29,659 53,213 64,881 Metals contracts 9,018 5,805 3,782 10,765 Total $ 79,073 $ 87,894 $ 118,004 $ 182,373

RECEIVABLES FROM BROKERS (Table

RECEIVABLES FROM BROKERS (Tables)	6 Months Ended
RECEIVABLES FROM BROKERS (Tables)	Jun. 30, 2017
Brokers and Dealers [Abstract]
Schedule of Receivable from Brokers	Amounts receivable from brokers consisted of the following as of (amounts in thousands): June 30, 2017 December 31, 2016 Required collateral $ 79,277 $ 55,868 Open foreign exchange positions 1,394 5,228 Total $ 80,671 $ 61,096

PROPERTY AND EQUIPMENT (Tables)

PROPERTY AND EQUIPMENT (Tables)	6 Months Ended
PROPERTY AND EQUIPMENT (Tables)	Jun. 30, 2017
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): June 30, 2017 December 31, 2016 Software $ 63,143 $ 52,891 Computer equipment 21,453 19,797 Leasehold improvements 11,360 11,055 Telephone equipment 783 778 Office equipment 2,119 2,138 Furniture and fixtures 2,332 2,285 Web site development costs 644 644 Gross property and equipment 101,834 89,588 Less: Accumulated depreciation and amortization (62,137 ) (53,126 ) Property and equipment, net $ 39,697 $ 36,462

INTANGIBLE ASSETS (Tables)

INTANGIBLE ASSETS (Tables)	6 Months Ended
INTANGIBLE ASSETS (Tables)	Jun. 30, 2017
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): June 30, 2017 December 31, 2016 Intangibles Gross Accumulated Net Gross Accumulated Net Customer lists $ 59,105 $ (26,325 ) $ 32,780 $ 50,253 $ (20,928 ) $ 29,325 Technology 71,353 (40,160 ) 31,193 70,145 (37,074 ) 33,071 Trademarks 7,442 (3,117 ) 4,325 7,104 (2,505 ) 4,599 Total finite lived intangibles 137,900 (69,602 ) 68,298 127,502 (60,507 ) 66,995 Trademark not subject to amortization (1) 363 — 363 363 — 363 Total intangibles $ 138,263 $ (69,602 ) $ 68,661 $ 127,865 $ (60,507 ) $ 67,358 (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 June 30, 2017 : Intangible Assets Amount (in thousands) Weighted average amortization period Customer lists $ 59,105 6.9 years Technology 71,353 9.0 years Trademarks (1) 7,805 6.7 years Total intangible assets $ 138,263 (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, 2016 $ 25,222 $ 4,519 $ 2,366 $ 32,107 Foreign currency translation adjustments 428 77 40 545 Carrying amount of goodwill as of June 30, 2017 $ 25,650 $ 4,596 $ 2,406 $ 32,652

OTHER ASSETS (Tables)

OTHER ASSETS (Tables)	6 Months Ended
OTHER ASSETS (Tables)	Jun. 30, 2017
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Schedule of Other Assets	Other assets consisted of the following as of (amounts in thousands): June 30, 2017 December 31, 2016 Vendor and security deposits $ 14,494 $ 9,670 Income tax receivable 4,565 1,017 Deferred tax assets, net 14,347 15,071 GTX trade receivables 4,232 7,515 Customer debit positions 8,505 9,781 Allowance on customer debit positions (8,338 ) (9,237 ) Insurance receivable 197 3,500 Prepaid assets 9,259 8,300 Miscellaneous receivables 5,963 6,615 Equity method investment 579 601 Total other assets $ 53,803 $ 52,833

NON-CONTROLLING INTERESTS (Tabl

NON-CONTROLLING INTERESTS (Tables)	6 Months Ended
NON-CONTROLLING INTERESTS (Tables)	Jun. 30, 2017
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, 2017 $ 6,594 Adjustment to the redemption value of non-controlling interests (983 ) Net income attributable to non-controlling interests 238 Distributions to non-controlling interest holders (873 ) June 30, 2017 $ 4,976

CONVERTIBLE SENIOR NOTES (Table

CONVERTIBLE SENIOR NOTES (Tables)	6 Months Ended
CONVERTIBLE SENIOR NOTES (Tables)	Jun. 30, 2017
Debt Disclosure [Abstract]
Schedule of Liability and Equity Components of Convertible Debt	The balances of the liability and equity components of the Convertible Senior Notes as of June 30, 2017 and December 31, 2016 were as follows (amounts in thousands): June 30, 2017 December 31, 2016 Liability component - principal $ 138,150 $ 138,150 Deferred bond discount (10,748 ) (13,213 ) Deferred financing cost (124 ) (168 ) Liability component - net carrying value $ 127,278 $ 124,769 Additional paid in capital $ 27,822 $ 27,822 Discount attributable to equity (419 ) (419 ) Equity component $ 27,403 $ 27,403
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/(Loss) was as follows (amounts in thousands): For the Three Months Ended June 30, For the Six Months Ended June 30, 2017 2016 2017 2016 Interest expense - stated coupon rate $ 1,425 $ 1,431 $ 2,850 $ 2,875 Interest expense - amortization of deferred bond discount and costs 1,269 1,091 2,509 2,156 Total interest expense - convertible senior notes $ 2,694 $ 2,522 $ 5,359 $ 5,031

EARNINGS_(LOSS) PER COMMON SH34

EARNINGS/(LOSS) PER COMMON SHARE (Tables)	6 Months Ended
EARNINGS/(LOSS) PER COMMON SHARE (Tables)	Jun. 30, 2017
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 June 30, For the Six Months Ended June 30, 2017 2016 2017 2016 Net income/(loss) applicable to GAIN Capital Holdings, Inc. $ 13,939 $ 10,841 $ (4,932 ) $ 19,193 Adjustment (1) 915 (1,690 ) 983 (1,591 ) Net income/(loss) available to GAIN common shareholders $ 14,854 $ 9,151 $ (3,949 ) $ 17,602 Weighted average common shares outstanding: Basic weighted average common shares outstanding 47,687,214 48,546,253 47,790,307 48,584,534 Effect of dilutive securities: Stock options 207,434 85,115 267,880 128,654 RSUs/RSAs — 105,820 6,923 147,345 Diluted weighted average common shares outstanding 47,894,648 48,737,188 47,790,307 48,860,533 Earnings/(loss) per common share: Basic $ 0.31 $ 0.19 $ (0.08 ) $ 0.36 Diluted $ 0.31 $ 0.19 $ (0.08 ) $ 0.36 (1) During the three and six months ended June 30, 2017 and 2016 , 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)	6 Months Ended
REGULATORY REQUIREMENTS (Tables)	Jun. 30, 2017
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 June 30, 2017 and the actual amounts of capital that were maintained (amounts in millions): Entity Name Minimum Capital Excess Percent of GAIN Capital Group, LLC $ 35.2 $ 45.5 $ 10.3 129 % GAIN Capital Securities, Inc. 0.1 0.4 0.3 400 % Trade Facts, Ltd. 0.6 3.1 2.5 517 % GAIN Capital-Forex.com Hong Kong, Ltd. 1.9 4.5 2.6 237 % GAIN Capital Australia Pty Ltd. 0.8 8.4 7.6 1,050 % GAIN Capital-Forex.com Canada Ltd. 0.2 1.3 1.1 650 % GAIN Capital-Forex.com U.K., Ltd. 5.1 16.7 11.6 327 % GAIN Capital Japan Co., Ltd. 1.3 8.9 7.6 685 % GAIN Global Markets, Inc. 0.8 1.4 0.6 175 % GAIN Capital UK, Ltd. 91.4 191.7 100.3 210 % GAIN Capital Singapore Pte, Ltd. 0.4 10.9 10.5 2,725 % Global Assets Advisors, LLC 0.1 1.4 1.3 1,400 % GAIN Capital Payments Ltd. 0.1 0.6 0.5 600 % Total $ 138.0 $ 294.8 $ 156.8 214 %

SEGMENT INFORMATION (Tables)

SEGMENT INFORMATION (Tables)	6 Months Ended
SEGMENT INFORMATION (Tables)	Jun. 30, 2017
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 June 30, Six Months Ended June 30, 2017 2016 2017 2016 Net revenue $ 80,605 $ 89,370 $ 120,691 $ 186,075 Employee compensation and benefits 16,630 16,897 31,978 33,599 Selling and marketing 7,244 6,546 16,149 12,760 Referral fees 9,826 13,699 22,149 30,301 Other operating expenses 15,978 20,749 30,460 41,628 Segment profit $ 30,927 $ 31,479 $ 19,955 $ 67,787 Institutional Three Months Ended June 30, Six Months Ended June 30, 2017 2016 2017 2016 Net revenue $ 7,690 $ 7,482 $ 16,311 $ 14,601 Employee compensation and benefits 3,588 3,462 7,630 6,664 Selling and marketing 10 35 31 41 Other operating expenses 2,928 2,518 6,155 4,959 Segment profit $ 1,164 $ 1,467 $ 2,495 $ 2,937 Futures Three Months Ended June 30, Six Months Ended June 30, 2017 2016 2017 2016 Net revenue $ 10,013 $ 12,857 $ 20,980 $ 25,060 Employee compensation and benefits 2,494 3,111 5,045 6,097 Selling and marketing 221 224 486 443 Referral fees 3,486 3,854 7,604 7,915 Other operating expenses 3,233 3,846 6,975 7,829 Segment profit $ 579 $ 1,822 $ 870 $ 2,776 Corporate and Other Three Months Ended June 30, Six Months Ended June 30, 2017 2016 2017 2016 Other revenue $ (254 ) $ (1,420 ) $ (362 ) $ (1,894 ) Employee compensation and benefits 3,964 3,145 6,489 6,648 Selling and marketing 52 — 116 — Other operating expenses 1,892 2,547 3,218 5,565 Loss $ (6,162 ) $ (7,112 ) $ (10,185 ) $ (14,107 )
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 June 30, Six Months Ended June 30, 2017 2016 2017 2016 Retail segment $ 30,927 $ 31,479 $ 19,955 $ 67,787 Institutional segment 1,164 1,467 2,495 2,937 Futures segment 579 1,822 870 2,776 Corporate and other (6,162 ) (7,112 ) (10,185 ) (14,107 ) SEGMENT PROFIT 26,508 27,656 13,135 59,393 Depreciation and amortization 4,340 3,559 8,359 6,712 Purchased intangible amortization 4,354 3,843 7,956 7,765 Restructuring expenses — 22 — 803 Integration expenses — 1,043 — 1,856 Legal settlement — — — 9,412 OPERATING PROFIT/(LOSS) 17,814 19,189 (3,180 ) 32,845 Interest expense on long term borrowings 2,694 2,560 5,359 5,152 INCOME/(LOSS) BEFORE INCOME TAX EXPENSE $ 15,120 $ 16,629 $ (8,539 ) $ 27,693

DESCRIPTION OF BUSINESS AND B37

DESCRIPTION OF BUSINESS AND BASIS OF PRESENTATION (Details)	6 Months Ended
DESCRIPTION OF BUSINESS AND BASIS OF PRESENTATION (Details)	Jun. 30, 2017segment
Accounting Policies [Abstract]
Number of operating segments	3

FAIR VALUE MEASUREMENT - Assets

FAIR VALUE MEASUREMENT - Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - Recurring - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total	$ 304,211	$ 378,096
Money market accounts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	83,962	120,927
US treasury bills: U.S. government and agency securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	69,910	135,974
Broker derivative contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	1,394	5,228
Certificates of deposit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	175	175
Other
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	125	115
Customer derivative contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities	148,645	115,677
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total	154,172	257,191
Level 1 \| Money market accounts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	83,962	120,927
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	69,910	135,974
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	175	175
Level 1 \| Other
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	125	115
Level 1 \| Customer derivative contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities	0	0
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total	150,039	120,905
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	1,394	5,228
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	148,645	115,677
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

FAIR VALUE MEASUREMENT - Carryi

FAIR VALUE MEASUREMENT - Carrying Value and Fair Value of Financial Assets and Liabilities (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Financial Assets:
Receivables from brokers	$ 80,671	$ 61,096
Financial Liabilities:
Convertible senior notes	127,278	124,769
Derivative Assets \| Level 1
Financial Assets:
Receivables from brokers	0	0
Derivative Assets \| Level 2
Financial Assets:
Receivables from brokers	79,277	55,868
Derivative Assets \| Level 3
Financial Assets:
Receivables from brokers	0	0
Derivative Assets \| Carrying Value
Financial Assets:
Receivables from brokers	79,277	55,868
Derivative Assets \| Fair Value
Financial Assets:
Receivables from brokers	79,277	55,868
Derivative Liabilities \| Level 1
Financial Liabilities:
Payables to customers	0	0
Convertible senior notes	0	0
Derivative Liabilities \| Level 2
Financial Liabilities:
Payables to customers	1,095,973	1,061,146
Convertible senior notes	124,568	122,544
Derivative Liabilities \| Level 3
Financial Liabilities:
Payables to customers	0	0
Convertible senior notes	0	0
Derivative Liabilities \| Carrying Value
Financial Liabilities:
Payables to customers	1,095,973	1,061,146
Convertible senior notes	127,278	124,769
Derivative Liabilities \| Fair Value
Financial Liabilities:
Payables to customers	1,095,973	1,061,146
Convertible senior notes	$ 124,568	$ 122,544

DERIVATIVES - Fair Value of Der

DERIVATIVES - Fair Value of Derivative Instruments (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Derivatives, Fair Value [Line Items]
Gross amounts of assets for derivative open positions at fair value	$ 230,925	$ 223,510
Gross amount of (liabilities) for derivative open positions at fair value	(80,886)	(102,605)
Net amounts of assets/(liabilities) for derivative open positions at fair value	150,039	120,905
Receivables from brokers	80,671	61,096
Payables to customers	(947,328)	(945,468)
Receivables from brokers
Derivatives, Fair Value [Line Items]
Receivables from brokers	80,671	61,096
Receivables from brokers \| Derivative Assets
Derivatives, Fair Value [Line Items]
Cash Collateral	79,277	55,868
Net amounts of assets/(liabilities) for derivative open positions at fair value	1,394	5,228
Payables to customers
Derivatives, Fair Value [Line Items]
Payables to customers	(947,328)	(945,468)
Payables to customers \| Derivative Liabilities
Derivatives, Fair Value [Line Items]
Cash Collateral	(1,095,973)	(1,061,145)
Net amounts of assets/(liabilities) for derivative open positions at fair value	148,645	115,677
Foreign currency exchange contracts
Derivatives, Fair Value [Line Items]
Gross amounts of assets for derivative open positions at fair value	133,897	130,301
Gross amount of (liabilities) for derivative open positions at fair value	(36,428)	(59,631)
Net amounts of assets/(liabilities) for derivative open positions at fair value	97,469	70,670
CFD contracts
Derivatives, Fair Value [Line Items]
Gross amounts of assets for derivative open positions at fair value	84,198	74,443
Gross amount of (liabilities) for derivative open positions at fair value	(40,818)	(37,241)
Net amounts of assets/(liabilities) for derivative open positions at fair value	43,380	37,202
Metal contracts
Derivatives, Fair Value [Line Items]
Gross amounts of assets for derivative open positions at fair value	12,830	18,766
Gross amount of (liabilities) for derivative open positions at fair value	(3,640)	(5,733)
Net amounts of assets/(liabilities) for derivative open positions at fair value	$ 9,190	$ 13,033

DERIVATIVES - Notional Values o

DERIVATIVES - Notional Values of Derivative Instruments (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Total contracts in long positions
Derivative [Line Items]
Notional amounts of derivative	$ 2,979,778	$ 2,540,571
Total contracts in long positions \| Foreign currency exchange contracts
Derivative [Line Items]
Notional amounts of derivative	2,848,711	2,427,066
Total contracts in long positions \| CFD contracts
Derivative [Line Items]
Notional amounts of derivative	129,973	112,685
Total contracts in long positions \| Metal contracts
Derivative [Line Items]
Notional amounts of derivative	1,094	820
Total contracts in short positions
Derivative [Line Items]
Notional amounts of derivative	4,792,311	2,445,035
Total contracts in short positions \| Foreign currency exchange contracts
Derivative [Line Items]
Notional amounts of derivative	4,613,766	2,288,386
Total contracts in short positions \| CFD contracts
Derivative [Line Items]
Notional amounts of derivative	178,136	156,308
Total contracts in short positions \| Metal contracts
Derivative [Line Items]
Notional amounts of derivative	$ 409	$ 341

DERIVATIVES - Net Gains (Losses

DERIVATIVES - Net Gains (Losses) on Derivatives (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Derivative [Line Items]
Net gains (losses) on derivative instruments, total	$ 79,073	$ 87,894	$ 118,004	$ 182,373
Foreign currency exchange contracts
Derivative [Line Items]
Net gains (losses) on derivative instruments	43,633	52,430	61,009	106,727
CFD contracts
Derivative [Line Items]
Net gains (losses) on derivative instruments	26,422	29,659	53,213	64,881
Metal contracts
Derivative [Line Items]
Net gains (losses) on derivative instruments	$ 9,018	$ 5,805	$ 3,782	$ 10,765

RECEIVABLES FROM BROKERS - Sche

RECEIVABLES FROM BROKERS - Schedule of Receivables from Brokers (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Receivables from Brokerage Clients [Line Items]
Receivables from brokers	$ 80,671	$ 61,096
Required collateral
Receivables from Brokerage Clients [Line Items]
Receivables from brokers	79,277	55,868
Open foreign exchange positions
Receivables from Brokerage Clients [Line Items]
Receivables from brokers	$ 1,394	$ 5,228

PROPERTY AND EQUIPMENT - Schedu

PROPERTY AND EQUIPMENT - Schedule of Property and Equipment (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Gross property and equipment	$ 101,834	$ 89,588
Less: Accumulated depreciation and amortization	(62,137)	(53,126)
Property and equipment, net	39,697	36,462
Software
Property, Plant and Equipment [Line Items]
Gross property and equipment	63,143	52,891
Computer equipment
Property, Plant and Equipment [Line Items]
Gross property and equipment	21,453	19,797
Leasehold improvements
Property, Plant and Equipment [Line Items]
Gross property and equipment	11,360	11,055
Telephone equipment
Property, Plant and Equipment [Line Items]
Gross property and equipment	783	778
Office equipment
Property, Plant and Equipment [Line Items]
Gross property and equipment	2,119	2,138
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Gross property and equipment	2,332	2,285
Website development costs
Property, Plant and Equipment [Line Items]
Gross property and equipment	$ 644	$ 644

PROPERTY AND EQUIPMENT - Additi

PROPERTY AND EQUIPMENT - Additional Information (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Property, Plant and Equipment [Abstract]
Depreciation and amortization expense	$ 4,340,000	$ 3,559,000	$ 8,359,000	$ 6,712,000
Additional depreciation charge due to change in useful life	$ 0	$ 200,000	$ 0	$ 400,000

INTANGIBLE ASSETS - Intangible

INTANGIBLE ASSETS - Intangible Assets (Details) $ in Thousands	Feb. 07, 2017$ / account	Jun. 30, 2017USD ($)	Jun. 30, 2016USD ($)	Jun. 30, 2017USD ($)	Jun. 30, 2016USD ($)	Dec. 31, 2016USD ($)
Intangible Assets by Major Class [Line Items]
Finite-lived intangible assets, gross		$ 137,900		$ 137,900		$ 127,502
Accumulated Amortization		(69,602)		(69,602)		(60,507)
Finite-lived intangible assets, net		68,298		68,298		66,995
Total intangibles, gross		138,263		138,263		127,865
Intangible assets, net		68,661		68,661		67,358
Payments to acquire intangible assets				6,960	$ 0
Amortization of Intangible Assets		4,354	$ 3,843	7,956	$ 7,765
Forex Capital Markets L.L.C.
Intangible Assets by Major Class [Line Items]
Intangible assets, net		100		100
Price per transferred account that executes new trade during 76 day period closing account transfer \| $ / account	500
Price per transferred account that executes new trade in 77 day period after initial period \| $ / account	250
Payments to acquire intangible assets				7,000
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		59,105		59,105		50,253
Accumulated Amortization		(26,325)		(26,325)		(20,928)
Finite-lived intangible assets, net		32,780		32,780		29,325
Total intangibles, gross		59,105		$ 59,105
Weighted average amortization period				6 years 11 months
Technology
Intangible Assets by Major Class [Line Items]
Finite-lived intangible assets, gross		71,353		$ 71,353		70,145
Accumulated Amortization		(40,160)		(40,160)		(37,074)
Finite-lived intangible assets, net		31,193		31,193		33,071
Total intangibles, gross		71,353		$ 71,353
Weighted average amortization period				9 years
Trademarks
Intangible Assets by Major Class [Line Items]
Finite-lived intangible assets, gross		7,442		$ 7,442		7,104
Accumulated Amortization		(3,117)		(3,117)		(2,505)
Finite-lived intangible assets, net		4,325		4,325		$ 4,599
Total intangibles, gross		$ 7,805		$ 7,805
Weighted average amortization period				6 years 8 months

INTANGIBLE ASSETS - Goodwill (D

INTANGIBLE ASSETS - Goodwill (Details)	6 Months Ended
INTANGIBLE ASSETS - Goodwill (Details)	Jun. 30, 2017USD ($)reporting_unit
Goodwill [Line Items]
Number of reporting units \| reporting_unit	3
Goodwill additions or impairments	$ 0
Goodwill	32,107,000
Goodwill [Roll Forward]
Goodwill. beginning balance	32,107,000
Foreign currency translation adjustments	545,000
Goodwill. ending balance	32,652,000
Operating Segments \| Retail
Goodwill [Line Items]
Goodwill	25,222,000
Goodwill [Roll Forward]
Goodwill. beginning balance	25,222,000
Foreign currency translation adjustments	428,000
Goodwill. ending balance	25,650,000
Operating Segments \| Institutional
Goodwill [Line Items]
Goodwill	4,519,000
Goodwill [Roll Forward]
Goodwill. beginning balance	4,519,000
Foreign currency translation adjustments	77,000
Goodwill. ending balance	4,596,000
Operating Segments \| Futures
Goodwill [Line Items]
Goodwill	2,366,000
Goodwill [Roll Forward]
Goodwill. beginning balance	2,366,000
Foreign currency translation adjustments	40,000
Goodwill. ending balance	$ 2,406,000

OTHER ASSETS - Schedule of Othe

OTHER ASSETS - Schedule of Other Assets (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Vendor and security deposits	$ 14,494	$ 9,670
Income tax receivable	4,565	1,017
Deferred tax assets, net	14,347	15,071
GTX trade receivables	4,232	7,515
Customer debit positions	8,505	9,781
Allowance on customer debit positions	(8,338)	(9,237)
Insurance receivable	197	3,500
Prepaid assets	9,259	8,300
Miscellaneous receivables	5,963	6,615
Equity method investment	579	601
Total other assets	$ 53,803	$ 52,833

RELATED PARTY TRANSACTIONS - Ad

RELATED PARTY TRANSACTIONS - Additional Information (Detail) - USD ($)	Jul. 28, 2017	Jun. 30, 2017	Dec. 31, 2016
Related Party Transaction [Line Items]
Payables to customers		$ 947,328,000	$ 945,468,000
Due from officers		600,000	0
Subsequent event
Related Party Transaction [Line Items]
Decrease due from officers	$ 600,000
Management
Related Party Transaction [Line Items]
Payables to customers		200,000	300,000
IPGL Limited
Related Party Transaction [Line Items]
Payables to customers		$ 13,300,000	$ 3,800,000

RESTRUCTURING (Details)

RESTRUCTURING (Details) - USD ($)	3 Months Ended		6 Months Ended
RESTRUCTURING (Details) - USD ($)	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Restructuring and Related Activities [Abstract]
Restructuring expenses	$ 0	$ 22,000	$ 0	$ 803,000

NON-CONTROLLING INTERESTS (Deta

NON-CONTROLLING INTERESTS (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016	Mar. 31, 2014
Increase (Decrease) in Temporary Equity [Roll Forward]
Redeemable noncontrolling interest, beginning balance			$ 6,594
Adjustment to the redemption value of non-controlling interests	$ (915)	$ 1,690	(983)	$ 1,591
Net income attributable to non-controlling interests	153	$ 745	238	$ 1,094
Distributions to non-controlling interest holders			(873)
Redeemable noncontrolling interest, ending balance	$ 4,976		$ 4,976
Global Assets 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%
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%

CONVERTIBLE SENIOR NOTES - Addi

CONVERTIBLE SENIOR NOTES - Additional Information (Details) - USD ($)	Nov. 27, 2013	Mar. 31, 2016	Jun. 30, 2017	Jun. 30, 2016	Apr. 01, 2015
Debt Instrument [Line Items]
Repurchase of convertible notes			$ 0	$ 1,735,000
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	$ 1,900,000
Stated interest rate (as percent)	4.125%
Proceeds from Convertible Debt	$ 77,900,000
Repurchase of convertible notes		$ 1,700,000

CONVERTIBLE SENIOR NOTES - Sche

CONVERTIBLE SENIOR NOTES - Schedule of Liability and Equity Components (Details) - Convertible Debt - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Liability component - principal	$ 138,150	$ 138,150
Deferred bond discount	(10,748)	(13,213)
Deferred financing cost	(124)	(168)
Liability component - net carrying value	127,278	124,769
Additional paid in capital	27,822	27,822
Discount attributable to equity	(419)	(419)
Equity component	$ 27,403	$ 27,403

CONVERTIBLE SENIOR NOTES - Sc54

CONVERTIBLE SENIOR NOTES - Schedule of Interest Expense (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Debt Instrument [Line Items]
Interest expense - amortization of deferred bond discount and costs			$ 221	$ 221
Convertible Debt
Debt Instrument [Line Items]
Interest expense - stated coupon rate	$ 1,425	$ 1,431	2,850	2,875
Interest expense - amortization of deferred bond discount and costs	1,269	1,091	2,509	2,156
Total interest expense - convertible senior notes	$ 2,694	$ 2,522	$ 5,359	$ 5,031

EARNINGS_(LOSS) PER COMMON SH55

EARNINGS/(LOSS) PER COMMON SHARE - Additional Information (Detail) - $ / shares shares in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive stock options excluded from calculation of diluted earnings per share	0.2	0.3	0.3	0.7
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]
Additional dilutive shares if indenture conditions were met			0.5
Convertible Notes Due 2020
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Additional dilutive shares if indenture conditions were met			1.5

EARNINGS_(LOSS) PER COMMON SH56

EARNINGS/(LOSS) PER COMMON SHARE - Computation of Earnings Per Share (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Earnings Per Share [Abstract]
Net income/(loss) applicable to GAIN Capital Holdings, Inc.	$ 13,939	$ 10,841	$ (4,932)	$ 19,193
Adjustment to fair value of redeemable non-controlling interests	915	(1,690)	983	(1,591)
Net income/(loss) available to GAIN common shareholders	$ 14,854	$ 9,151	$ (3,949)	$ 17,602
Weighted average common shares outstanding:
Basic weighted average common shares outstanding	47,687,214	48,546,253	47,790,307	48,584,534
Effect of dilutive securities:
Stock options (in shares)	207,434	85,115	267,880	128,654
RSUs/RSAs (in shares)	0	105,820	6,923	147,345
Diluted weighted average common shares outstanding	47,894,648	48,737,188	47,790,307	48,860,533
Earnings/(loss) per common share:
Basic (usd per share)	$ 0.31	$ 0.19	$ (0.08)	$ 0.36
Diluted (usd per share)	$ 0.31	$ 0.19	$ (0.08)	$ 0.36

LEGAL - Additional Information

LEGAL - Additional Information (Detail) $ in Millions	12 Months Ended
LEGAL - Additional Information (Detail) $ in Millions	Dec. 31, 2016USD ($)
Cameron Farley Ltd
Long-term Purchase Commitment [Line Items]
Payments for legal settlements	$ 9.2

INCOME TAXES - Additional Infor

INCOME TAXES - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Income Tax Disclosure [Abstract]
Provision (benefit) for income taxes	$ 994	$ 5,025	$ (3,899)	$ 7,372
Effective income tax rates (as percent)	6.60%	30.20%	45.70%	26.60%

REGULATORY REQUIREMENTS - Regul

REGULATORY REQUIREMENTS - Regulatory Capital Subsidiaries Required to Maintain (Detail) $ in Millions	Jun. 30, 2017USD ($)
Schedule Of Compliance With Regulatory Capital Requirements For Broker Dealer [Line Items]
Minimum Regulatory Capital Requirements	$ 138
Capital Levels Maintained	294.8
Excess Net Capital	$ 156.8
Percent of Requirement Maintained	214.00%
GAIN Capital Group, LLC
Schedule Of Compliance With Regulatory Capital Requirements For Broker Dealer [Line Items]
Minimum Regulatory Capital Requirements	$ 35.2
Capital Levels Maintained	45.5
Excess Net Capital	$ 10.3
Percent of Requirement Maintained	129.00%
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%
Trade Facts, Ltd.
Schedule Of Compliance With Regulatory Capital Requirements For Broker Dealer [Line Items]
Minimum Regulatory Capital Requirements	$ 0.6
Capital Levels Maintained	3.1
Excess Net Capital	$ 2.5
Percent of Requirement Maintained	517.00%
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	4.5
Excess Net Capital	$ 2.6
Percent of Requirement Maintained	237.00%
GAIN Capital Australia Pty Ltd.
Schedule Of Compliance With Regulatory Capital Requirements For Broker Dealer [Line Items]
Minimum Regulatory Capital Requirements	$ 0.8
Capital Levels Maintained	8.4
Excess Net Capital	$ 7.6
Percent of Requirement Maintained	1050.00%
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	1.3
Excess Net Capital	$ 1.1
Percent of Requirement Maintained	650.00%
GAIN Capital-Forex.com U.K., Ltd.
Schedule Of Compliance With Regulatory Capital Requirements For Broker Dealer [Line Items]
Minimum Regulatory Capital Requirements	$ 5.1
Capital Levels Maintained	16.7
Excess Net Capital	$ 11.6
Percent of Requirement Maintained	327.00%
GAIN Capital Japan Co., Ltd.
Schedule Of Compliance With Regulatory Capital Requirements For Broker Dealer [Line Items]
Minimum Regulatory Capital Requirements	$ 1.3
Capital Levels Maintained	8.9
Excess Net Capital	$ 7.6
Percent of Requirement Maintained	685.00%
GAIN Global Markets, Inc.
Schedule Of Compliance With Regulatory Capital Requirements For Broker Dealer [Line Items]
Minimum Regulatory Capital Requirements	$ 0.8
Capital Levels Maintained	1.4
Excess Net Capital	$ 0.6
Percent of Requirement Maintained	175.00%
GAIN Capital UK, Ltd.
Schedule Of Compliance With Regulatory Capital Requirements For Broker Dealer [Line Items]
Minimum Regulatory Capital Requirements	$ 91.4
Capital Levels Maintained	191.7
Excess Net Capital	$ 100.3
Percent of Requirement Maintained	210.00%
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	10.9
Excess Net Capital	$ 10.5
Percent of Requirement Maintained	2725.00%
Global Assets Advisors, LLC
Schedule Of Compliance With Regulatory Capital Requirements For Broker Dealer [Line Items]
Minimum Regulatory Capital Requirements	$ 0.1
Capital Levels Maintained	1.4
Excess Net Capital	$ 1.3
Percent of Requirement Maintained	1400.00%
GAIN Capital Payments Ltd.
Schedule Of Compliance With Regulatory Capital Requirements For Broker Dealer [Line Items]
Minimum Regulatory Capital Requirements	$ 0.1
Capital Levels Maintained	0.6
Excess Net Capital	$ 0.5
Percent of Requirement Maintained	600.00%

SEGMENT INFORMATION - Additiona

SEGMENT INFORMATION - Additional Information (Detail) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017USD ($)	Jun. 30, 2016USD ($)	Jun. 30, 2017USD ($)segmentmarket	Jun. 30, 2016USD ($)
Segment Reporting [Abstract]
Number of operating segments \| segment			3
Number of accessible global financial markets \| market			12,500
Intersegment Eliminations
Segment Reporting Information [Line Items]
Net revenue \| $	$ (0.6)	$ (0.3)	$ (1.1)	$ (0.7)

SEGMENT INFORMATION - Selected

SEGMENT INFORMATION - Selected Financial Information by Segment (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Employee compensation and benefits	$ 26,325	$ 26,615	$ 50,540	$ 53,008
Selling and marketing	7,527	6,805	16,783	13,244
Referral fees	13,312	17,553	29,753	38,216
Segment profit (loss)	26,508	27,656	13,135	59,393
Operating Segments \| Retail
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Net revenue	80,605	89,370	120,691	186,075
Employee compensation and benefits	16,630	16,897	31,978	33,599
Selling and marketing	7,244	6,546	16,149	12,760
Referral fees	9,826	13,699	22,149	30,301
Other operating expenses	15,978	20,749	30,460	41,628
Segment profit (loss)	30,927	31,479	19,955	67,787
Operating Segments \| Institutional
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Net revenue	7,690	7,482	16,311	14,601
Employee compensation and benefits	3,588	3,462	7,630	6,664
Selling and marketing	10	35	31	41
Other operating expenses	2,928	2,518	6,155	4,959
Segment profit (loss)	1,164	1,467	2,495	2,937
Operating Segments \| Futures
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Net revenue	10,013	12,857	20,980	25,060
Employee compensation and benefits	2,494	3,111	5,045	6,097
Selling and marketing	221	224	486	443
Referral fees	3,486	3,854	7,604	7,915
Other operating expenses	3,233	3,846	6,975	7,829
Segment profit (loss)	579	1,822	870	2,776
Corporate and Other
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Net revenue	(254)	(1,420)	(362)	(1,894)
Employee compensation and benefits	3,964	3,145	6,489	6,648
Selling and marketing	52	0	116	0
Other operating expenses	1,892	2,547	3,218	5,565
Segment profit (loss)	$ (6,162)	$ (7,112)	$ (10,185)	$ (14,107)

SEGMENT INFORMATION - Reconcili

SEGMENT INFORMATION - Reconciliation of Operating Segment Profit to Income Before Income Tax Expense (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
SEGMENT PROFIT	$ 26,508,000	$ 27,656,000	$ 13,135,000	$ 59,393,000
Depreciation and amortization	4,340,000	3,559,000	8,359,000	6,712,000
Purchased intangible amortization	4,354,000	3,843,000	7,956,000	7,765,000
Restructuring expenses	0	22,000	0	803,000
Integration expenses	0	1,043,000	0	1,856,000
Legal settlement	0	0	0	9,412,000
OPERATING PROFIT/(LOSS)	17,814,000	19,189,000	(3,180,000)	32,845,000
Interest expense on long term borrowings	2,694,000	2,560,000	5,359,000	5,152,000
INCOME/(LOSS) BEFORE INCOME TAX EXPENSE/(BENEFIT)	15,120,000	16,629,000	(8,539,000)	27,693,000
Operating Segments \| Retail
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
SEGMENT PROFIT	30,927,000	31,479,000	19,955,000	67,787,000
Operating Segments \| Institutional
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
SEGMENT PROFIT	1,164,000	1,467,000	2,495,000	2,937,000
Operating Segments \| Futures
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
SEGMENT PROFIT	579,000	1,822,000	870,000	2,776,000
Corporate and Other
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
SEGMENT PROFIT	$ (6,162,000)	$ (7,112,000)	$ (10,185,000)	$ (14,107,000)

SUBSEQUENT EVENTS - Additional

SUBSEQUENT EVENTS - Additional Information (Detail) - Subsequent event - USD ($)	Aug. 03, 2017	Aug. 02, 2017
Subsequent Event [Line Items]
Common stock dividend declared (usd per share)	$ 0.06
Line of credit \| Revolving credit facility
Subsequent Event [Line Items]
Maximum amount under facility		$ 50,000,000
Line of credit \| Revolving credit facility \| Maximum
Subsequent Event [Line Items]
Amount of increase in credit facility available upon request		25,000,000
Line of credit \| Revolving credit facility \| Minimum
Subsequent Event [Line Items]
Amount of increase in credit facility available upon request		$ 5,000,000