Global Brokerage (GLBR) 10-Q 7 Nov 14 2014 Q3 Quarterly report Financial data

Document_And_Entity_Informatio

Document And Entity Information	9 Months Ended
	Sep. 30, 2014	Nov. 06, 2014	Nov. 06, 2014
		Class A common stock	Class B common stock
Document Information [Line Items]	'	'	'
Entity Registrant Name	'FXCM Inc.	'	'
Entity Central Index Key	'0001499912	'	'
Current Fiscal Year End Date	'--12-31	'	'
Entity Filer Category	'Accelerated Filer	'	'
Document Type	'10-Q	'	'
Document Period End Date	30-Sep-14	'	'
Document Fiscal Year Focus	'2014	'	'
Document Fiscal Period Focus	'Q3	'	'
Trading Symbol	'FXCM	'	'
Amendment Flag	'false	'	'
Entity Common Stock, Shares Outstanding	'	47,160,590	34

Condensed_Consolidated_Stateme

Condensed Consolidated Statements of Financial Condition (USD $)	Sep. 30, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Current assets	'	'
Cash and cash equivalents	$326,730	$365,245
Cash and cash equivalents, held for customers	1,332,399	1,190,880
Restricted time deposits	3,648	0
Trading securities	633	0
Due from brokers	32,960	5,450
Accounts receivable and other receivables, net	20,344	19,806
Deferred tax asset	5,215	11,910
Total current assets	1,721,929	1,593,291
Restricted time deposits	5,472	0
Deferred tax asset	174,309	166,576
Office, communication and computer equipment, net	48,438	49,165
Goodwill	326,100	307,936
Other intangible assets, net	66,224	76,713
Notes receivable	9,608	5,950
Other assets	32,329	24,316
Total assets	2,384,409	2,223,947
Current liabilities	'	'
Customer account liabilities	1,332,399	1,190,880
Accounts payable and accrued expenses	56,773	69,697
Credit agreement	30,000	0
Notes payable	7,460	9,800
Due to brokers	916	8,652
Securities sold, not yet purchased	3,815	0
Deferred tax liability	218	0
Due to related parties pursuant to tax receivable agreement	20,276	18,588
Total current liabilities	1,451,857	1,297,617
Deferred tax liability	3,078	3,687
Due to related parties pursuant to tax receivable agreement	131,562	131,670
Senior convertible notes	150,236	146,303
Other liabilities	6,052	9,289
Total liabilities	1,742,785	1,588,566
Commitments and Contingencies (see Note 15)	'	'
Stockholdersb Equity	'	'
Additional paid-in capital	260,231	245,426
Retained earnings	9,485	16,352
Accumulated other comprehensive loss	-7,487	-5,344
Total stockholdersb equity FXCM Inc.	262,692	256,882
Non-controlling interests	378,932	378,499
Total stockholdersb equity	641,624	635,381
Total liabilities and stockholdersb equity	2,384,409	2,223,947
Class A common stock	'	'
Stockholdersb Equity	'	'
Common stock	462	447
Class B common stock	'	'
Stockholdersb Equity	'	'
Common stock	$1	$1

Condensed_Consolidated_Stateme1

Condensed Consolidated Statements of Financial Condition (Parenthetical) (USD $)	Sep. 30, 2014	Dec. 31, 2013
Class A common stock	'	'
Common stock, par value	$0.01	$0.01
Common stock, shares authorized	3,000,000,000	3,000,000,000
Common stock, shares issued	46,204,590	44,664,884
Common stock, shares outstanding	46,204,590	44,664,884
Class B common stock	'	'
Common stock, par value	$0.01	$0.01
Common stock, shares authorized	1,000,000	1,000,000
Common stock, shares issued	34	41
Common stock, shares outstanding	34	41

Condensed_Consolidated_Stateme2

Condensed Consolidated Statements of Operations (USD $)	3 Months Ended		9 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Revenues	'	'	'	'
Retail trading revenue	$87,826	$86,974	$244,222	$282,296
Institutional trading revenue	24,417	22,856	72,354	82,204
Trading revenue	112,243	109,830	316,576	364,500
Interest income	637	537	1,893	1,886
Brokerage interest expense	-199	-63	-459	-187
Net interest revenue	438	474	1,434	1,699
Other income	3,466	2,944	11,072	10,046
Total net revenues	116,147	113,248	329,082	376,245
Operating Expenses	'	'	'	'
Compensation and benefits	27,572	28,809	86,283	78,929
Allocation of net income to Lucid members for services provided	1,483	2,996	6,771	18,000
Total compensation and benefits	29,055	31,805	93,054	96,929
Referring broker fees	20,998	20,709	56,615	64,481
Advertising and marketing	5,071	6,305	18,652	19,813
Communication and technology	13,434	10,111	37,684	28,231
Trading costs, prime brokerage and clearing fees	8,021	6,809	24,257	23,708
General and administrative	17,219	27,949	48,898	53,843
Depreciation and amortization	15,041	12,849	40,793	37,304
Total operating expenses	108,839	116,537	319,953	324,309
Total operating income (loss)	7,308	-3,289	9,129	51,936
Other Expense	'	'	'	'
Loss on equity method investments, net	376	183	910	728
Interest on borrowings	3,028	2,869	9,121	4,976
Income (loss) before income taxes	3,904	-6,341	-902	46,232
Income tax provision	1,144	2,444	1,648	16,793
Net income (loss)	2,760	-8,785	-2,550	29,439
Net income (loss) attributable to FXCM Inc.	2,392	-5,122	1,391	11,862
Weighted average shares of Class A common stock outstanding:	'	'	'	'
Basic (in shares)	42,963	33,718	40,108	30,983
Diluted (in shares)	43,819	34,469	42,367	32,009
Net income (loss) per share attributable to stockholders of Class A common stock of FXCM Inc.:	'	'	'	'
Basic (in dollars per share)	$0.06	($0.15)	$0.03	$0.38
Diluted (in dollars per share)	$0.05	($0.15)	$0.03	$0.37
Dividends declared per common share (in dollars per share)	$0.06	$0.06	$0.18	$0.18
Other Non-controlling Interests	'	'	'	'
Other Expense	'	'	'	'
Net income attributable to non-controlling interest	-1,170	-530	-5,697	-3,613
FXCM Holdings, LLC	'	'	'	'
Other Expense	'	'	'	'
Net income attributable to non-controlling interest	$1,538	($3,133)	$1,756	$21,190

Condensed_Consolidated_Stateme3

Condensed Consolidated Statements of Comprehensive Income (USD $)	3 Months Ended		9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest [Abstract]	'	'	'	'
Net income (loss)	$2,760	($8,785)	($2,550)	$29,439
Other comprehensive (loss) income	'	'	'	'
Foreign currency translation (loss) gain	-8,366	5,171	-3,643	-7,563
Income tax (benefit) expense	-58	19	108	-108
Other comprehensive (loss) income, net of tax	-8,308	5,152	-3,751	-7,455
Comprehensive (loss) income	-5,548	-3,633	-6,301	21,984
Comprehensive (loss) income attributable to FXCM Inc.	-2,278	-2,448	-752	8,963
Other Non-controlling Interests	'	'	'	'
Other comprehensive (loss) income	'	'	'	'
Comprehensive income attributable to non-controlling interest	-1,185	-530	-5,712	-3,613
FXCM Holdings, LLC	'	'	'	'
Other comprehensive (loss) income	'	'	'	'
Comprehensive income attributable to non-controlling interest	($2,085)	($655)	$163	$16,634

Condensed_Consolidated_Stateme4

Condensed Consolidated Statement of Stockholders' Equity (USD $)	Total	Non-controlling Interests	Retained Earnings	Accumulated Other Comprehensive Loss	Additional Paid-in Capital	Class A common stock	Class A common stock	Class B common stock
In Thousands, except Share data, unless otherwise specified	USD ($)	USD ($)	USD ($)	USD ($)	USD ($)		Common Stock	Common Stock
							USD ($)	USD ($)
Beginning Balance at Dec. 31, 2013	$635,381	$378,499	$16,352	($5,344)	$245,426	'	$447	$1
Beginning Balance (in shares) at Dec. 31, 2013	'	'	'	'	'	'	44,664,884	41
Increase (Decrease) in Stockholders' Equity [Roll Forward]	'	'	'	'	'	'	'	'
Net (loss) income	-2,550	-3,941	1,391	'	'	'	'	'
Other comprehensive loss, net of tax	-3,751	-1,608	'	-2,143	'	'	'	'
Comprehensive (loss) income	-6,301	-5,549	1,391	-2,143	'	'	'	'
Repurchase of Class A common stock	-644	-175	'	'	-469	'	'	'
Repurchase of Class A common stock (in shares)	'	'	'	'	'	'	-45,985	'
Equity based compensation	11,098	5,662	'	'	5,435	'	1	'
Equity based compensation (in shares)	648,490	'	'	'	'	'	163,832	'
Dividends on Class A common stock	-8,258	'	-8,258	'	'	'	'	'
Exchange of Holdings units to Class A common stock (see Note 9)	0	-6,328	'	'	6,317	'	11	'
Exchange of Holdings units to Class A common stock (See Note 9) (in shares)	'	'	'	'	'	'	1,155,359	-6
Assignment of permitted transferees	0	'	'	'	'	'	'	'
Assignment of permitted transferees (in shares)	'	'	'	'	'	'	'	-1
Stock options exercised	3,608	1,080	'	'	2,525	'	3	'
Stock options exercised (in shares)	266,500	'	'	'	'	267,000	266,500	'
Effects of Tax Receivable Agreement	997	'	'	'	997	'	'	'
Contributions - other non-controlling interests	10,819	10,819	'	'	'	'	'	'
Distributions - non-controlling members	-5,076	-5,076	'	'	'	'	'	'
Ending Balance at Sep. 30, 2014	$641,624	$378,932	$9,485	($7,487)	$260,231	'	$462	$1
Ending Balance (In shares) at Sep. 30, 2014	'	'	'	'	'	'	46,204,590	34

Condensed_Consolidated_Stateme5

Condensed Consolidated Statements of Cash Flows (USD $)	9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
			Faros	Faros	Noncontrolling Interest	Noncontrolling Interest
Cash Flows From Operating Activities	'	'	'	'	'	'
Net income (loss)	($2,550)	$29,439	'	'	'	'
Adjustments to reconcile net (loss) income to net cash (used in) provided by operating activities	'	'	'	'	'	'
Depreciation and amortization	40,793	37,304	'	'	'	'
Equity-based compensation	10,238	9,896	'	'	'	'
Deferred tax expense	5,051	10,982	'	'	'	'
Gain on Follow-on Payment	-3,672	0	'	'	'	'
Loss on disposal of fixed assets	10	126	'	'	'	'
Amortization of deferred bond discount	3,933	1,644	'	'	'	'
Amortization of deferred financing cost	1,381	815	'	'	'	'
Loss on equity investment	910	728	'	'	'	'
Remeasurement of tax receivable agreement liability	-360	0	'	'	'	'
Changes in operating assets and liabilities	'	'	'	'	'	'
Cash and cash equivalents, held for customers	-140,468	-73,145	'	'	'	'
Restricted time deposits	-9,120	0	'	'	'	'
Trading securities	-633	0	'	'	'	'
Due from brokers	-27,510	7,135	'	'	'	'
Accounts receivable, net	-1,393	-3,570	'	'	'	'
Tax receivable	-5,160	2,973	'	'	'	'
Other assets	-960	2,623	'	'	'	'
Customer account liabilities	141,519	73,503	'	'	'	'
Accounts payable and accrued expenses	-13,829	26,607	'	'	'	'
Other liabilities	436	728	'	'	'	'
Payments for tax receivable agreement	-3,707	-4,079	'	'	'	'
Due to brokers	-7,736	18,583	'	'	'	'
Securities sold, not yet purchased	3,815	0	'	'	'	'
Foreign currency remeasurement gain (loss)	345	-1,513	'	'	'	'
Net cash (used in) provided by operating activities	-8,667	140,779	'	'	'	'
Cash Flows From Investing Activities	'	'	'	'	'	'
Purchases of office, communication and computer equipment	-16,320	-16,792	'	'	'	'
Purchase of intangible assets	-9,789	-35	'	'	'	'
Acquisition of business, net of cash acquired	-21,791	-26,812	'	'	'	'
Issuance of notes receivable	-1,500	0	'	'	'	'
Payments for equity investment	0	-3,000	'	'	'	'
Net cash (used) in investing activities	-49,400	-46,639	'	'	'	'
Cash Flows From Financing Activities	'	'	'	'	'	'
Distributions - non-controlling members	-4,281	-10,621	'	'	'	'
Contributions from other non-controlling members	2,540	0	'	'	'	'
Dividends paid	-8,258	-6,923	'	'	'	'
Proceeds from exercise of stock options	3,608	21,877	'	'	'	'
Stock repurchase	-644	-16,312	'	'	'	'
Proceeds from issuance of senior convertibles notes, net	0	166,467	'	'	'	'
Purchase of convertible note hedges	0	-29,101	'	'	'	'
Proceeds from sale of warrants	0	18,578	'	'	'	'
Borrowings under the credit agreement	60,000	10,000	'	'	'	'
Payments on borrowings under the credit agreement	-30,000	-95,000	'	'	'	'
Net cash provided by financing activities	22,965	58,965	'	'	'	'
Effect of foreign currency exchange rate changes on cash and cash equivalents	-3,413	-3,492	'	'	'	'
Net (decrease) increase in cash and cash equivalents	-38,515	149,613	'	'	'	'
Cash and Cash Equivalents	'	'	'	'	'	'
Beginning of year	365,245	272,332	'	'	'	'
End of period	326,730	421,945	'	'	'	'
Supplemental disclosures of cash flow activities	'	'	'	'	'	'
Cash paid for taxes	407	3,199	'	'	'	'
Cash paid for interest	2,762	1,207	'	'	'	'
Supplemental disclosure of non-cash investing activities	'	'	'	'	'	'
Notes receivable credited towards consideration for acquisition of business	11,942	0	'	'	'	'
Supplemental disclosure of non-cash financing activities	'	'	'	'	'	'
Exchange of Holdings Units for shares of Class A common stock	6,328	45,792	'	'	'	'
Business acquisition consideration payable	0	15,300	'	'	'	'
Notes issued for non-controlling interest	8,279	0	'	'	'	'
Non-cash distribution, non-controlling interest	'	'	0	15,569	795	0
Follow-on Payment for business acquisition	$0	$10,631	'	'	'	'

Description_of_Business_and_Ba

Description of Business and Basis of Presentation	9 Months Ended
	Sep. 30, 2014
Accounting Policies [Abstract]	'
Description of Business and Basis of Presentation	'
	Description of Business and Basis of Presentation
	Description of Business
	FXCM Inc. (the “Corporation”), a Delaware holding company, is an online provider of foreign exchange (“FX”) trading and related services to retail and institutional customers worldwide. The Corporation operates through its managing membership interest in FXCM Holdings, LLC (“Holdings”), the Corporation’s sole operating asset. Holdings is a majority-owned, controlled and consolidated subsidiary of the Corporation. As used in these notes, the term “Company” collectively refers to the Corporation, Holdings and subsidiaries of Holdings.
	Basis of Presentation
	Basis of Consolidation
	The accompanying condensed consolidated financial statements are presented in accordance with accounting principles generally accepted in the United States of America (“U.S. GAAP”). The Company consolidates those entities in which it is the primary beneficiary of a variable-interest entity ("VIE") as required by Financial Accounting Standards Board (“FASB”) Accounting Standards Codification Topic (“ASC”) 810, Consolidations (“ASC 810”), or entities where it has a controlling interest. Intercompany accounts and transactions are eliminated in consolidation.
	As indicated above, the Corporation operates and controls all of the businesses and affairs of Holdings and its subsidiaries. As such, the Corporation consolidates the financial results of Holdings and records a non-controlling interest for the economic interest in Holdings not owned by the Corporation. The Corporation’s and the non-controlling unit holders’ economic interest in Holdings was 56.4% and 43.6%, respectively, as of September 30, 2014. The Corporation’s and the non-controlling unit holders’ economic interest in Holdings was 54.8% and 45.2%, respectively, as of December 31, 2013.
	Net income attributable to the non-controlling interest in Holdings in the condensed consolidated statements of operations represents the portion of earnings or loss attributable to the economic interest in Holdings held by the non-controlling unit holders. Net income attributable to other non-controlling interests in the condensed consolidated statements of operations represents the portion of net income or loss attributable to the non-controlling interests of Lucid Markets Trading Limited ("Lucid"), Faros Trading LLC ("Faros"), V3 Markets, LLC ("V3") (see Note 3) and other consolidated entities. Net income attributable to the non-controlling interest in Lucid represents the portion of earnings or loss attributable to the 49.9% economic interest held by Lucid non-controlling members whose allocation among the non-controlling members is not contingent upon services being provided. The portion of the 49.9% of Lucid earnings allocated among the non-controlling members of Lucid contingent on services provided is reported as a component of compensation expense under Allocation of net income to Lucid members for services provided in the condensed consolidated statements of operations. Net income or loss attributable to the non-controlling interests in Faros and V3 represent the portion of earnings or loss attributable to the 49.9% economic interest held by Faros and V3 non-controlling members. Net income or loss attributable to the non-controlling interests in other consolidated entities represents the portion of earnings or loss attributable to the economic interests held by the non-controlling members.
	Non-controlling interests in the condensed consolidated statements of financial condition represents the portion of equity attributable to the non-controlling interests of Holdings, Lucid, Faros, V3 and other consolidated entities. The allocation of equity to non-controlling interests is based on the percentage owned by the non-controlling interest in the respective entity.
	The Company’s condensed consolidated financial statements include the following significant subsidiaries of Holdings:
	Forex Capital Markets L.L.C.	(“US”)
	FXCM Asia Limited	(“HK”)
	Forex Capital Markets Limited	(“UK LTD”)
	FXCM Australia Limited	(“Australia”)
	ODL Group Limited	(“ODL”)
	FXCM Securities Limited	(“FSL”)
	FXCM Japan Securities Co., Ltd.	(“FXCMJ”)
	FXCM UK Merger Limited	(“Merger”)
	Lucid Markets Trading Limited	(“Lucid”)
	Lucid Markets LLP	("Lucid LLP")
	Faros Trading LLC	("Faros")
	V3 Markets, LLC	("V3")
	Investments where the Company is deemed to exercise significant influence, but no control, are accounted for using the equity method of accounting. The Company records its pro-rata share of earnings or losses each period and records any dividends as a reduction in the investment balance. The carrying value of these investments are included in Other assets in the condensed consolidated statements of financial condition and earnings or losses are included in Loss on equity method investments, net in the condensed consolidated statements of operations.
	Use of Estimates
	The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the condensed consolidated financial statements as well as the reported amount of revenue and expenses during the year. Actual results could differ from those estimates and could have a material impact on the consolidated financial statements.
	Reclassifications
	Certain reclassifications have been made to previously reported amounts to conform to the current presentation.
	Interim Financial Statements
	The Company believes that the condensed consolidated interim financial statements reflect all adjustments of a normal recurring nature and disclosures that are necessary for a fair presentation of the results for the interim periods presented. The results of operations for the interim period are not necessarily indicative of the results of operations to be expected for the full year. The interim 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 for the year ended December 31, 2013. As permitted under Rule 10-01 of the Securities and Exchange Commission Regulation S-X, certain notes or other financial information are condensed or omitted in the interim condensed consolidated financial statements.
	Accounting Pronouncement Adopted in 2014
	Obligations Resulting from Joint and Several Liability Arrangements
	In February 2013, the FASB issued Accounting Standards Update ("ASU") No. 2013-04, Obligations Resulting from Joint and Several Liability Arrangements for Which the Total Amount of the Obligation is Fixed at the Reporting Date. This standard requires an entity to measure obligations resulting from joint and several liability arrangements for which the total amount of the obligation is fixed at the reporting date as the sum of (i) the amount the entity agreed to pay on the basis of its arrangement among its co-obligors and (ii) any additional amount it expect to pay on behalf of its co-obligors.
	This guidance became effective for the Company on January 1, 2014 and did not have a material impact on the presentation of the Company’s unaudited condensed consolidated financial statements.
	Parent's Accounting for the Cumulative Translation Adjustment upon Derecognition of an Investment within a Foreign Entity or of an Investment in a Foreign Entity
	In March 2013, the FASB issued ASU No. 2013-05, Parent's Accounting for the Cumulative Translation Adjustment upon Derecognition of Certain Subsidiaries or Groups of Assets within a Foreign Entity or of an Investment in Foreign Entity. This standard addresses whether consolidation guidance or foreign currency guidance applies to the release of the cumulative translation adjustment into net income when a parent sells all or a part of its investment in a foreign entity or no longer holds a controlling financial interest in a subsidiary or net assets that are a business (other than a sale of in-substance real estate) within a foreign entity. The standard also resolves the diversity in practice for the cumulative translation adjustment treatment in business combinations achieved in stages involving foreign entities.
	Under this standard, the entire amount of the cumulative translation adjustment associated with the foreign entity should be released into earnings when there has been: (i) a sale of a subsidiary or group of net assets within a foreign entity and the sale represents a complete or substantially complete liquidation of the foreign entity in which the subsidiary or the net assets had resided; (ii) a loss of a controlling financial interest in an investment in a foreign entity; or (iii) a change in accounting method from applying the equity method to an investment in a foreign entity to consolidating the foreign entity.
	This guidance became effective for the Company on January 1, 2014 and did not have a material impact on the presentation of the Company’s unaudited condensed consolidated financial statements.
	Presentation of Unrecognized Tax Benefits
	In July 2013, the FASB issued ASU No. 2013-11, Presentation of Unrecognized Tax Benefits When a Net Operating Loss Carryforward, a Similar Tax Loss, or a Tax Credit Carryforward Exists. This standard requires a liability related to unrecognized tax benefits to be presented as a reduction to the related deferred tax asset for a net operating loss carryforward or a tax credit carryforward. When the carryforwards are not available at the reporting date under the tax law of the applicable jurisdiction or the tax law of the applicable jurisdiction does not require, and the entity does not intend to use, the deferred tax asset for such purpose, the unrecognized tax benefit will be presented in the financial statements as a liability and will not be combined with the related deferred tax asset.
	This guidance became effective for the Company on January 1, 2014 and did not have a material impact on the presentation of the Company’s unaudited condensed consolidated financial statements.
	Recently Issued Accounting Pronouncements
	Reporting Discontinued Operations
	In April 2014, the FASB issued ASU No. 2014-08, Presentation of Financial Statements (Topic 205) and Property, Plant, and Equipment (Topic 360): Reporting Discontinued Operations and Disclosures of Disposals of Components of an Entity. Under this standard, a discontinued operation will include a disposal of a major part of an entity’s operations and financial results such as a separate major line of business or a separate major geographical area of operations. The standard also raises the threshold to be a major operation but no longer precludes discontinued operations presentation where there is significant continuing involvement or cash flows with a disposed component of an entity. The standard expands disclosures to include cash flows where there is significant continuing involvement with a discontinued operation and the pre-tax profit or loss of disposal transactions not reported as discontinued operations. The standard is effective prospectively for years beginning on or after December 15, 2014, with early application permitted. The Company plans to adopt the standard prospectively on its required effective date of January 1, 2015 and the impact, if any, on the Company’s consolidated financial condition, results of operations or cash flows will be dependent on the nature of future disposals.
	Revenue from Contracts with Customers
	In May 2014, the FASB issued ASU No. 2014-09, Revenue from Contracts with Customers. The standard states that an entity should recognize revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. The standard sets out the following five steps an entity should apply to achieve this core principle.
	•Identify the contract(s) with a customer.
	•Identify the performance obligations in the contract.
	•Determine the transaction price.
	•Allocate the transaction price to the performance obligations in the contract.
	•Recognize revenue when (or as) the entity satisfies a performance obligation.
	For a public entity, the standard is effective for annual reporting periods beginning after December 15, 2016, including interim periods within that reporting period. Early application is not permitted. The Company is currently evaluating the impact this standard will have on its consolidated financial condition, results of operations, cash flows and disclosures and is currently unable to estimate the impact of adopting this guidance.

Holdings

Holdings	9 Months Ended
	Sep. 30, 2014
Noncontrolling Interest [Abstract]	'
Holdings	'
	Holdings
	The Corporation consolidates the financial results of Holdings whereby it records a non-controlling interest for the economic interest in Holdings not owned by the Corporation. Pursuant to an agreement between the Corporation and Holdings, anytime the Corporation cancels, issues or repurchases shares of its Class A common stock, Holdings enters into an equivalent Holdings unit transaction with the Corporation so that at all times the number of shares of Class A common stock is equal to the Corporation's membership units in Holdings. In addition, anytime Holdings unit holders (other than the Corporation) exchange their units for shares of the Corporation’s Class A common stock, Holdings is required to transfer an equal amount of units to the Corporation.
	Changes in the non-controlling and the Corporation’s interests in Holdings for the nine months ended September 30, 2014 are presented in the following table:
		Controlling Units		Non-Controlling Units		Total Units		FXCM Inc.		Non-Controlling		Total
	Balance as of January 1, 2014	44,664,884		36,835,821		81,500,705		54.8	%	45.2	%	100	%
	Holdings units acquired by FXCM Inc. related to exchanges of Holdings units for shares of Class A common stock	1,155,359		(1,155,359	)	—		1.4	%	(1.4	)%	—	%
	Holding units repurchased related to Class A common stock repurchased	(45,985	)	—		(45,985	)	—	%	—	%	—	%
	Exercise of stock options	266,500		—		266,500		0.1	%	(0.1	)%	—	%
	Issuance under equity based compensation	163,832		—		163,832		0.1	%	(0.1	)%	—	%
	Balance as of September 30, 2014	46,204,590		35,680,462		81,885,052		56.4	%	43.6	%	100	%

Business_Acquisition

Business Acquisition	9 Months Ended
	Sep. 30, 2014
Business Combinations [Abstract]	'
Business Acquisition	'
	Business Acquisition
	V3
	On January 21, 2014 (the "V3 Acquisition Date"), the Company, through a new entity, V3, created with the non-controlling members of Lucid, completed the acquisition of certain assets of Infinium Capital Holdings LLC ("Infinium") and certain of its affiliates. The acquisition expands the Lucid business model into a broader array of financial instruments and provides more robust connectivity to various financial exchanges. The consideration for the acquisition was approximately $32.5 million consisting of cash, assumed liabilities and the credit of $12.1 million of Infinium senior secured notes plus interest held and exchanged by a subsidiary of the Company. The Company holds a controlling 50.1% interest in V3.
	The acquisition was accounted for in accordance with ASC 805, Business Combinations ("ASC 805"). The assets acquired and the non-controlling interest were recorded at their estimated fair values in accordance with ASC 820, Fair Value Measurement ("ASC 820") at the V3 Acquisition Date. Full goodwill of $20.2 million was calculated as the fair value of estimated consideration over the estimated fair value of the net assets acquired. The estimated fair value of the non-controlling interest was $16.2 million and was determined by the fair value of the consideration. Goodwill was allocated at the reporting unit level in the Institutional segment based on an analysis of the fair value of assets acquired. V3 is included in the Institutional segment for purposes of segment reporting (see Note 20).
	Subsequent to the acquisition date, the purchase price was decreased by $0.9 million, due to the final determination of the assumed liabilities. In connection with this purchase price adjustment, the initial goodwill recorded was reduced by $0.8 million to $19.4 million.
	V3 Purchase Price Allocation (¹)
	(Amounts in thousands)
	Purchase price				$	15,825
	Non-Controlling interest				15,762
	Total fair value at Acquisition Date				31,587
	Net assets acquired	$	10,210
	Adjustments to reflect acquired assets and liabilities at fair value
	Trading platform (2)	950
	Processing platform (3)	150
	Non-compete agreement (4)	450
	Executory contract (5)	470
	Fair value of net assets acquired				12,230
	Goodwill resulting from the V3 acquisition				$	19,357
	__________________
		(1)	The amounts included in the V3 Purchase Price Allocation table represent the allocation of the purchase price and includes revisions made during the 12 month remeasurement period from the V3 Acquisition Date.
		(2)	Consists of internally developed software platforms that support trade execution, with an amortization life of 4 years.
		(3)	Consists of an internally developed software platform that supports trading, with an amortization life of 5 years.
		(4)	Amortization life is 1 year.
		(5)	Consists of a service agreement relating to fiber optics, wireless and other services, with an amortization life of 3 years.
	The amounts included in the V3 Purchase Price Allocation table represent the preliminary allocation of the purchase price and are subject to revision during the measurement period, a period not to exceed 12 months from the V3 Acquisition Date. Adjustments to the provisional values during the measurement period will be pushed back to the date of acquisition. Comparative information for periods after acquisition but before the period in which the adjustments were identified will be adjusted to reflect the effects of the adjustments as if they were taken into account as of the acquisition date. Changes to the amounts recorded as assets and liabilities will result in a corresponding adjustment to goodwill.
	Condensed Statement of Net Assets Acquired
	The following condensed statement of net assets acquired reflects the amounts of V3 net assets recognized as of the V3 Acquisition Date, with amounts in thousands:
		As of January 21, 2014
	Assets
	Office, communication and computer equipment, net	$	973
	Intangible assets	2,020
	Exchange memberships and common equity shares	6,429
	Equity method investments, net	1,523
	Other assets	1,392
	Total assets	$	12,337
	Liabilities	(107		)
	Fair value of net assets acquired	$	12,230
	Condensed Combined Financial Information:
	The following condensed financial information presents the resulting operations of V3 from the V3 Acquisition Date to September 30, 2014, with amounts in thousands:
		For the period
		January 21, 2014 to
		30-Sep-14
	Total revenue	$	14,384
	Net loss	$	(2,052	)
	Faros
	On September 20, 2013 (the “Faros Acquisition Date”), the Company acquired a 50.1% controlling interest in Faros. Faros is a global leader in foreign exchange intelligence, market coverage, and execution services to the institutional foreign exchange market. The acquisition further expands the Company's presence and capabilities in the institutional marketplace. As consideration, the Company provided an initial cash payment of $5.0 million (the “Initial Payment”) and a follow-on payment (the “ Follow-on Payment”) to be made in 2015 in an amount to be determined, based on the purchase agreement (the “Faros Purchase Agreement”) estimated at $10.6 million on the Faros Acquisition Date for a total estimated purchase price of $15.6 million. Pursuant to the terms of the Faros Purchase Agreement, the Follow-on Payment is payable partly in shares of the Corporation’s Class A common stock to one of the Faros sellers if certain criteria are met. Under the terms of the Faros Purchase Agreement, any of the Corporation’s Class A common stock issued to the Faros seller will be restricted for sale until September 2021 if the Faros seller ceases to be employed by Faros as of either December 31, 2015 or December 31, 2016 for reasons other than death, disability or the sale of the majority of the Corporation’s combined voting power. This restriction ("Faros Liquidity Restriction") has an estimated fair value of $0.4 million and is accounted for as deferred compensation and recognized over the term of the restriction.
	The Company has the option to buy out the remaining interest of the Faros sellers subject to the terms of the Faros Purchase Agreement. In the event the buyout is not exercised by the Company by December 31, 2017, the sellers have the right to market Faros for sale of all the membership interests of Faros.
	The fair value of the Follow-on Payment is included in Other liabilities in the condensed consolidated statements of financial condition. Changes in the fair value of the Follow-on Payment subsequent to the Faros Acquisition Date are recognized in earnings in the period in which the change is recorded. The Company estimated the fair value of the Follow-on Payment using both a discounted cash flow model and guideline public company model. This fair value measurement is based on significant inputs not observed in the market and thus represents Level III instruments as defined by ASC 820 (see Note 17). The discount rate considered in the assessment of the $10.6 million Follow-on Payment at the Faros Acquisition Date was 25.0%. In December 2013, the Company recorded a reduction to the Follow-on Payment of $6.9 million. In March 2014, the Company reduced the Follow-on Payment by the remaining $3.7 million. The $3.7 million decrease in the estimated fair value of the Follow-on Payment was recorded in Other income in the condensed consolidated statements of operations. The decline in the estimated fair value of the Follow-on Payment is due to lowering our Faros earnings before income taxes and depreciation ("EBITDA") estimate. The Company reassessed the Follow-on Payment liability at September 30, 2014 and determined that a fair value of zero was still appropriate.
	The Acquisition was accounted for in accordance with ASC 805. The assets acquired, liabilities assumed and non-controlling interest were recorded at their estimated fair values in accordance with ASC 820 at the Acquisition Date as summarized in the table below. Full goodwill of $23.0 million was calculated as the fair value of estimated consideration over the estimated fair value of the net assets acquired. The estimated fair value of the non-controlling interest was $15.6 million, and was determined by valuing Faros using a discounted cash flow model and guideline public company model, less the Initial Payment and the Follow-on Payment. The estimate of the fair value of the non-controlling interest is based on an assumed discount rate of 25.0%, long term annual earnings growth rate of 3.0% and assumed adjustments due to the lack of control that market participants would consider when estimating the fair value of the non-controlling interest in Faros. Goodwill was allocated at the reporting unit level in the Institutional segment based on an analysis of the fair value of assets acquired and expected future benefits of synergies created from combining the Faros market making business with the Company's foreign exchange trading expertise. Faros is included in the Institutional segment for purposes of segment reporting (see Note 20).
	Faros Purchase Price Allocation
	(Amounts in thousands)
	Purchase price				$	15,631
	Non-Controlling interest				15,569
	Total fair value at Acquisition Date				31,200
	Net assets acquired	$	137
	Adjustments to reflect acquired assets and liabilities at fair value
	Customer relationships (1)	6,000
	Non-compete agreement (2)	1,900
	Trade name (3)	130
	Fair value of net assets acquired				8,167
	Goodwill resulting from the Faros acquisition				$	23,033
	__________________
	(1)	Consists of institutional and bank customers, with an amortization life of 4 years.
(2)	Amortization life is 9 years.
(3)	Amortization life is 3 year.
The amounts included in the Faros Purchase Price Allocation table represent the preliminary allocation of the purchase price as well as revisions made during the measurement period, a period not to exceed 12 months from the Faros Acquisition Date. Adjustments to the provisional values during the measurement period were pushed back to the date of acquisition. Comparative information for periods after acquisition but before the period in which the adjustments were identified were adjusted to reflect the effects of the adjustments as if they were taken into account as of the acquisition date. Changes to the amounts recorded as assets and liabilities resulted in a corresponding adjustment to goodwill.
Condensed Statement of Net Assets Acquired
The following condensed statement of net assets acquired reflects the amounts of Faros net assets recognized as of the Faros Acquisition Date, with amounts in thousands:
	As of September 20, 2013
Assets
Cash and cash equivalents	$	1,055
Accounts receivable, net	40
Office, communication and computer equipment, net	31
Intangible assets	8,030
Other assets	76
Total assets	$	9,232
Liabilities
Accounts payable and accrued expenses	$	1,065
Total liabilities	$	1,065
Fair value of net assets acquired	$	8,167
Contingencies and Accounts Receivable
There were no contingent liabilities recorded in the fair value of net assets acquired as of the Faros Acquisition Date and the fair value of net assets acquired includes accounts receivables with book value that approximates fair value. There was no reserve netted against receivables as of the Faros Acquisition Date. The Company has collected all material accounts receivable amounts as of September 30, 2014.
Pro Forma Condensed Combined Financial Information
The Company's pro forma condensed combined financial information for the acquisitions completed in 2014 (i.e. V3), and 2013 (i.e., Faros) are presented as they may have appeared if all acquisitions had been completed on January 1, 2014 and 2013, with amounts in thousands:
	Three Months Ended September 30,						Nine Months Ended September 30,
	2014			2013			2014			2013
Total revenue	$	116,147		$	124,181		$	329,082		$	416,843
Net income (loss) before non-controlling interest	$	2,760		$	(9,249	)	$	(4,615	)	$	33,856
These pro forma results for nine months ended September 30, 2014 and 2013 primarily include the related tax impact as well as the adjustments for the intangible assets acquired.
Acquisition-related Costs
Acquisition-related transaction costs for the V3 acquisition were nil and $1.2 million for the three and nine months ended September 30, 2014, respectively. Acquisition-related transaction costs for the three and nine months ended September 30, 2013 were not material. Acquisition-related transaction costs are included in General and administrative expense in the condensed consolidated statements of operations.

Restricted_Time_Deposits

Restricted Time Deposits	9 Months Ended
	Sep. 30, 2014
Cash and Cash Equivalents [Abstract]	'
Restricted Time Deposits	'
	Restricted Time Deposits
	During the quarter ended September 30, 2014, FXCMJ established a $3.6 million, 0.025%, three months time deposit and a $5.5 million, 0.025%, one year time deposit with Sumitomo Mitsui Banking Corporation (“SMBC”). The time deposits secure a letter of guarantee issued by SMBC on behalf of FXCMJ and may be withdrawn under limited circumstances subject to the financial covenants of the letter of guarantee. As a result of the restriction on withdrawal, the time deposits are presented separately in the condensed consolidated statements of financial condition.

Trading_Securities

Trading Securities	9 Months Ended
	Sep. 30, 2014
Investments, Debt and Equity Securities [Abstract]	'
Trading Securities	'
	Trading Securities
	Equity securities purchased with the intent to sell in the near-term are classified as trading securities and are carried at their fair value based on the quoted market prices of the securities in active markets. As of September 30, 2014 and December 31, 2013, trading securities amounted to $0.6 million and nil, respectively.
	Net realized and unrealized gains and losses on trading securities are included in Institutional trading revenue in the condensed consolidated statements of operations. For the purpose of determining realized gains and losses, the cost of securities sold is based on specific identification.
	For the three and nine months ended September 30, 2014, net realized and unrealized gains or losses related to trading securities were gains of $2.3 million and $3.3 million, respectively. There were no realized or unrealized gains or losses related to trading securities for the three and nine months ended September 30, 2013.

Accounts_Receivable_and_Other_

Accounts Receivable and Other Receivables	9 Months Ended
	Sep. 30, 2014
Receivables [Abstract]	'
Accounts Receivable and Other Receivables	'
	Accounts Receivable and Other Receivables
	Accounts and other receivables consisted of the following:
		September 30, 2014	December 31, 2013
	Accounts receivable, net	11,323	9,953
	Notes receivable	—	5,992
	Tax receivable	9,021	3,861
	Total accounts and other receivables	20,344	19,806

Equity_Method_Investments

Equity Method Investments	9 Months Ended
	Sep. 30, 2014
Equity Method Investments and Joint Ventures [Abstract]	'
Equity Method Investments	'
	Equity Method Investments
	On December 4, 2012, the Company completed the acquisition of a non-controlling equity interest in an electronic communication network for foreign exchange trading. As the Company holds a 35.3% equity interest and exerts significant influence, the investment is accounted for using the equity method and is included in the institutional segment for purposes of segment reporting (see Note 20). The Company also has a 21.8% equity interest in a developer of FX trading software which is accounted for using the equity method and is included in the corporate segment for purposes of segment reporting.
	In conjunction with the V3 acquisition on January 21, 2014, the Company acquired a 66.3% non-controlling interest in a limited liability company ("LLC") that holds a 17.26% interest in a firm that delivers investment information to investment professionals. As of September 30, 2014, the other members of the LLC had not yet consented to the transfer of the 66.3% non-controlling interest to the Company. Until such consent is received, the Company is only entitled to its share of profits, losses and distributions and the Company does not have any right to participate in the management of the business and affairs of the LLC, including participating in major decisions. Accordingly, the Company’s interest is accounted for using the equity method and is included in the institutional segment for purposes of segment reporting (see Note 20).
	As of September 30, 2014 and December 31, 2013, the Company’s carrying values of equity method investments were $10.4 million and $9.8 million, respectively, and are included as a component of Other assets in the condensed consolidated statements of financial condition.
	Loss on equity method investments was $0.4 million and $0.9 million for the three and nine months ended September 30, 2014, respectively, and is included in Loss on equity method investments, net in the condensed consolidated statements of operations. Loss on equity method investments was $0.2 million and $0.7 million for the three and nine months ended September 30, 2013, respectively, and is included in Loss on equity method investments, net in the condensed consolidated statements of operations.
	The Company did not receive any dividend distributions from its equity method investments during the three and nine months ended September 30, 2014. Dividends received from the Company's equity method investments during the three and nine months ended September 30, 2013 were not material.

Earnings_per_Share

Earnings per Share	9 Months Ended
	Sep. 30, 2014
Earnings Per Share [Abstract]	'
Earnings per Share	'
	Earnings per Share
	Basic earnings per share (“EPS”) measures the performance of an entity over the reporting period. Diluted EPS measures the performance of an entity over the reporting period while giving effect to all potentially dilutive instruments that were outstanding during the period. The Company uses the treasury stock method in accordance with ASC 260, Earnings per Share (“ASC 260”), to determine diluted EPS.
	In accordance with ASC 260, all outstanding unvested share-based payments that contain rights to non-forfeitable dividends participate in the undistributed earnings with the common stockholders and are therefore participating securities. The shares of Class B common stock do not share in the earnings of the Company and are therefore not participating securities. Accordingly, basic and diluted net earnings per share of Class B common stock have not been presented.
	During the nine months ended September 30, 2014 and 2013, stock options granted to certain employees, non-employees and independent directors in the aggregate of 1,039,490 and 7,611,390, respectively, were not included in the computation of earnings per common share because they were antidilutive under the treasury method.
	The Company issued 7.2 million shares of the Corporation’s Class A common stock in connection with the Lucid acquisition subject to the achievement of certain targets related to the financial performance of Lucid (the "Profit Targets"). The Lucid sellers achieved the Profit Targets for the first anniversary shares during the quarter ended June 30, 2013 and received 1.2 million shares in June 2013. During the nine months ended September 30, 2014, the Lucid sellers achieved the Profit Targets for the 3.0 million second anniversary shares and these shares are included in the computation of basic and diluted EPS for the three and nine months ended September 30, 2014. If the third anniversary Profit Targets are achieved, the Lucid sellers are entitled to receive 3.0 million shares on the third anniversary of the acquisition date of June 18, 2012. In accordance with ASC 260, the third anniversary shares are considered contingently issuable shares. Accordingly, the third anniversary shares are considered outstanding common shares and included in basic EPS as of the date that all necessary conditions to receiving the shares have been satisfied (that is, when issuance of the shares is no longer contingent) and there is no circumstance under which those shares would not be issued. In accordance with ASC 260, shares are included in diluted EPS if all necessary conditions have been satisfied by the end of the period.
	As described in Note 14, in June 2013 FXCM Inc. issued $172.5 million principal amount of 2.25% senior convertible notes maturing on June 15, 2018 (the “Convertible Notes”). The Convertible Notes will be convertible at an initial conversion rate of 53.2992 shares of the Corporation's Class A common stock per $1,000 principal amount of the Convertible Notes, which is equivalent to an initial conversion price of approximately $18.76. In accordance with ASC 260, the shares of the Corporation's Class A common stock issuable upon conversion of the Convertible Notes are included in the calculation of diluted EPS to the extent that the conversion value of the securities exceeds the principal amount. For diluted EPS purposes, the number of shares of the Corporation's Class A common stock that is necessary to settle such excess is considered issued. For the three and nine months ended September 30, 2014, the conversion value did not exceed the principal amount and therefore the conversion effect was not included in the computation of diluted EPS because it was antidilutive under the treasury method.
	As described in Note 14, the Company also entered into a warrant transaction whereby the Company sold to the counterparties warrants to purchase shares of the Corporation's Class A common stock. For the three and nine months ended September 30, 2014, the warrants were not included in the computation of diluted EPS because they were antidilutive under the treasury method.
	Additionally, the non-controlling members of Holdings have the right to exchange their Holdings units for shares of the Corporation’s Class A common stock on a one-for-one basis at fair value, subject to customary conversion rate adjustments for stock splits, stock dividends and reclassifications. These shares were also excluded from the computation of dilutive EPS because they were antidilutive under the treasury method. During the three and nine months ended September 30, 2014, certain members of Holdings exchanged 0.1 million and 1.2 million, respectively, of their Holdings units, on a one-for-one basis, for shares of Class A common stock of the Corporation.
	The following is a reconciliation of the numerator and denominator used in the basic and diluted EPS calculations, with amounts in thousands except per share data:
		Three Months Ended September 30,					Nine Months Ended September 30,
		2014		2013			2014		2013
	Basic and diluted net income (loss) per share:
	Numerator
	Net income (loss) available to holders of Class A common stock	$	2,392	$	(5,122	)	$	1,391	$	11,862
	Earnings allocated to participating securities	—		—			—		—
	Earnings available for common stockholders	$	2,392	$	(5,122	)	$	1,391	$	11,862
	Denominator for basic net income per share of Class A common stock
	Weighted average shares of Class A common stock	42,963		33,718			40,108		30,983
	Add dilutive effect of the following:
	Weighted average of Lucid's first anniversary shares issued on June 18, 2013	—		—			—		738
	Weighted average of Lucid's second anniversary shares issued on June 18, 2014	—		—			1,381		—
	Stock options	856		751			878		288
	Convertible note hedges	—		—			—		—
	Warrants	—		—			—		—
	Dilutive weighted average shares of Class A common stock	43,819		34,469			42,367		32,009
	Basic income (loss) per share of Class A common stock	$	0.06	$	(0.15	)	$	0.03	$	0.38
	Diluted income (loss) per share of Class A common stock	$	0.05	$	(0.15	)	$	0.03	$	0.37

Related_Party_Transactions

Related Party Transactions	9 Months Ended
	Sep. 30, 2014
Related Party Transactions [Abstract]	'
Related Party Transactions	'
	Related Party Transactions
	Amounts receivable from, and payable to, related parties are set forth below, with amounts in thousands:
		30-Sep-14		December 31, 2013
	Receivables
	Advances to Holdings non-controlling members	$	305	$	940
	Accounts receivable - Lucid non-controlling members	968		—
	Notes receivable and interest - Lucid non-controlling members	8,203		—
	Advances to employees	720		826
		$	10,196	$	1,766
	Payables
	Guarantee agreement ("Monetary Guaranty")	$	6,561	$	8,363
	Employees	1,797		708
	Shareholders with greater than 5% ownership in the Company	—		200
	Due to Lucid non-controlling members in connection with the allocation of net income to Lucid non-controlling members for services provided	7,159		9,826
	Due to Lucid non-controlling members in connection with trade settlements	—		169
	Notes payable to Lucid non-controlling members in connection with the acquisition	7,460		9,800
	Tax receivable agreement	151,838		150,257
	Follow-on Payment	—		3,672
		$	174,815	$	182,995
	The Company has advanced funds for withholding taxes to several non-controlling members of Holdings. The outstanding balance as of September 30, 2014 and December 31, 2013, included in the table above, is included in Accounts receivable, net in the condensed consolidated statements of financial condition.
	As described in Note 3, V3 was formed by the Company and the non-controlling members of Lucid. The Company contributed capital of approximately $16.3 million and the non-controlling members of Lucid contributed capital of approximately $16.2 million. The non-controlling members of Lucid borrowed approximately $8.1 million from the Company to assist with funding their portion of the capital contribution, which is included in Notes receivable in the condensed consolidated statements of financial condition as of September 30, 2014. The amount borrowed is due in 2017 and bears interest at the rate of 2% per annum. Interest income related to the notes receivable was not material for the three and nine months ended September 30, 2014 and nil for the three and nine months ended September 30, 2013.
	Included in Accounts receivable in the condensed consolidated statements of financial condition is an additional $0.2 million for the Lucid non-controlling members’ capital contributions in connection with the V3 acquisition and $0.8 million of advances to the Lucid non-controlling members.
	The Company has advanced funds to several employees. The outstanding balances as of September 30, 2014 and December 31, 2013, included in the table above, are included in Accounts receivable, net in the condensed consolidated statements of financial condition.
	Customer account liabilities in the condensed consolidated statements of financial condition include balances for employees and shareholders with greater than 5% ownership in the Company.
	UK LTD is party to an arrangement with Global Finance Company (Cayman) Limited (“Global Finance”) and Master Capital Group, S.A.L. (“Master Capital”). A shareholder of the Company beneficially owns more than 90% of the equity of Global Finance and Master Capital. Pursuant to such arrangement, Global Finance and Master Capital are permitted to use the brand name “FXCM” and our technology platform to act as the Company’s local presence in certain countries in the Middle East and North Africa (“MENA”). UK collects and remits to Global Finance and Master Capital fees and commissions charged by Global Finance and Master Capital to customers in MENA countries. For the three and nine months ended September 30, 2014, these fees and commissions were approximately $0.3 million and $0.9 million, respectively, and are included in the condensed consolidated statements of operations in Referring broker fees. For the three and nine months ended September 30, 2013 these fees and commissions were approximately $0.4 million and$1.2 million, respectively, and are included in Referring broker fees in the condensed consolidated statements of operations. As of September 30, 2014, the shareholder described above beneficially owns less than 5% of the Corporation's Class A common stock.
	In August 2012, the Company entered into a master guaranty agreement (the “Method Guaranty”) with Method Credit Fund (“Method”), a Cayman Island company, owned by certain directors and shareholders of the Company, including several of the Company’s executive officers. Pursuant to the Method Guaranty, Method unconditionally guaranteed the obligations of certain counterparties that maintained a margin account with the Company. The Method Guaranty required Method to maintain a cash collateral account held by the Company equal to the aggregate amount of margin extended to all counterparties covered by the Method Guaranty. In exchange for this unconditional guaranty, the Company remitted a fee to Method determined on a counterparty by counterparty basis which was agreed upon by the Company, Method and the respective counterparty. The agreement was terminated in November 2013 and upon termination, the aggregate amount of margin extended under the Method Guaranty was reduced to zero. As of September 30, 2014 and December 31, 2013, the aggregate amount of margin extended under the Method Guaranty was zero. During the three and nine months ended September 30, 2013, no payments were made by Method to the Company to satisfy a guaranteed counterparty obligation. For the three and nine months ended September 30, 2013, fees collected from counterparties and subsequently remitted to Method by the Company were not material and are included in Referring broker fees in the condensed consolidated statements of operations.
	In November 2013, the Company entered into a master guaranty agreement (the “Monetary Guaranty”) with Monetary Credit Group LLC (“Monetary”), a newly formed Texas limited liability company, owned by certain directors and shareholders of the Company, including several of the Company’s executive officers. Pursuant to the Monetary Guaranty, Monetary unconditionally guarantees the obligations of certain counterparties that maintain a margin account with the Company. The Monetary Guaranty requires Monetary to maintain a cash collateral account held by the Company equal to the aggregate amount of margin extended to all counterparties covered by the Monetary Guaranty. In exchange for this unconditional guaranty, the Company remits a fee to Monetary determined on a counterparty by counterparty basis which is agreed upon by the Company, Monetary and the respective counterparty. The Monetary Guaranty may be terminated by either the Company or Monetary at any time provided that if Monetary elects to terminate there are no guaranteed obligations outstanding. As of September 30, 2014 and December 31, 2013, the aggregate amount of margin extended under the Monetary Guaranty was $12.9 million and $4.5 million, respectively. During the three and nine months ended September 30, 2014, no payments were made by Monetary to the Company to satisfy a guaranteed counterparty obligation. For the three and nine months ended September 30, 2014, fees collected from counterparties and subsequently remitted to Monetary by the Company under the Monetary Guaranty were $0.3 million and $0.5 million, respectively, and are included in Referring broker fees in the condensed consolidated statements of operations. As of September 30, 2014 and December 31, 2013, the Company held cash collateral related to the Monetary Guaranty in the amount of $6.6 million and $8.4 million, respectively, which is included in Cash and cash equivalents, held for customers and Customer account liabilities in the condensed consolidated statements of financial condition.
	Accounts payable and accrued expenses in the condensed consolidated statements of financial condition include a balance of nil and $0.2 million of advances from certain Lucid non-controlling members as of September 30, 2014 and December 31, 2013, respectively. Accounts payable and accrued expenses also include $7.2 million and $9.8 million related to the Allocation of net income to Lucid members for services provided as of September 30, 2014 and December 31, 2013, respectively (see Note 1).
	Notes payable of $7.5 million and $9.8 million, included in the condensed consolidated statements of financial condition as of September 30, 2014 and December 31, 2013, respectively, represent the amount borrowed from the Lucid non-controlling members in connection with the Lucid acquisition. Interest expense related to the unsecured promissory notes was not material for the three and nine months ended September 30, 2014 and 2013 (see Note 14).
	Other liabilities in the condensed consolidated statements of financial condition include the Faros Follow-on Payment of nil and $3.7 million as of September 30, 2014 and December 31, 2013, respectively (see Note 3).
	Exchange Agreement
	The members of Holdings (other than the Corporation) entered into an exchange agreement under which they (or certain permitted transferees thereof) have the right (subject to the terms of the exchange agreement as described therein), to exchange their Holdings units for shares of the Corporation’s Class A common stock on a one-for-one basis at fair value, subject to customary conversion rate adjustments for stock splits, stock dividends and reclassifications. During the nine months ended September 30, 2014 and 2013, certain members of Holdings exchanged 1.2 million and 8.6 million, respectively, of their Holdings units, on a one-for-one basis, for shares of Class A common stock of the Corporation pursuant to the exchange agreement.
	Payments under Tax Receivable Agreement
	The Corporation entered into a tax receivable agreement with the members of Holdings (other than the Corporation) that will provide for the payment by the Corporation to Holdings’ members (other than the Corporation) as defined therein. The aggregate payments due under the tax receivable agreement were $151.8 million and $150.3 million as of September 30, 2014 and December 31, 2013, respectively. During the nine months ended September 30, 2014, payments of $3.7 million were made pursuant to the tax receivable agreement.

StockBased_Compensation

Stock-Based Compensation	9 Months Ended
	Sep. 30, 2014
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]	'
Stock-Based Compensation	'
	Stock-Based Compensation
	The Company has a long term incentive plan (the “LTIP”) that provides for the grant of stock options to purchase shares of the Corporation’s Class A common stock to its employees (“Employee Stock Options”) and the independent members of the board of directors (“Independent Directors Options”) (collectively, the “Stock Options”). The Employee Stock Options have a contractual term of seven years and a four-year graded vesting schedule. The Independent Directors Options also have a seven-year contractual term but vest on the first anniversary after the grant date. Under the terms of the LTIP, the Company may issue new shares or treasury shares upon share option exercise.
	During the nine months ended September 30, 2014, the Company granted 83,490 Independent Director Options and 565,000 Employee Stock Options.
	The following table summarizes the Company’s stock options activity as of September 30, 2014 and changes for the nine months then ended:
	Options		Shares			Weighted-				Weighted-
						Average Exercise Price				Average Remaining Contractual Term
	Outstanding at January 1, 2014		7,607,800			$	13.48			4.3
	Granted		648,490			$	16.28
	Exercised		(266,500	)		$	13.54
	Forfeited or expired		(209,900	)		$	13.1
	Outstanding as of September 30, 2014		7,779,890			$	13.72			3.81
	Vested or expected to vest at September 30, 2014		7,704,862			$	13.73			3.81
	Exercisable as of September 30, 2014		4,632,150			$	13.52			3.43
	The weighted-average grant date fair value of options granted during the nine months ended September 30, 2014 and 2013 was $5.66 and $5.52, respectively.
	As of September 30, 2014 the weighted average period over which compensation cost on non-vested Stock Options is expected to be recognized is 2.2 years and the unrecognized expense is $7.5 million. The fair value of the shares vested under the LTIP during the nine months ended September 30, 2014 and 2013 was $2.2 million and $1.8 million, respectively. Stock-based compensation before income taxes included in Compensation and benefits in the condensed consolidated statements of operations was $2.6 million and $7.5 million for the three and nine months ended September 30, 2014, respectively, for the Employee Stock Options. Stock-based compensation before income taxes included in compensation and benefits in the condensed consolidated statements of operations was $2.5 million and $7.2 million for the three and nine months ended September 30, 2013, respectively, for the Employee Stock Options. Stock-based compensation before income taxes included in Compensation and benefits in the condensed consolidated statements of operations was $0.1 million and $0.3 million for the three and nine months ended September 30, 2014, respectively, for the Independent Directors Options. Stock-based compensation before income taxes included in Compensation and benefits in the condensed consolidated statements of operations was not material and $0.3 million for the three and nine months ended September 30, 2013, respectively, for the Independent Directors Options. The total compensation cost capitalized and included in Office, communication and computer equipment, net in the condensed consolidated statements of financial condition was $0.9 million and $1.4 million as of September 30, 2014 and December 31, 2013, respectively.
	In arriving at stock-based compensation expense, the Company estimates the number of stock-based awards that will be forfeited due to employee turnover. The Company’s forfeiture assumption is based primarily on its turn-over historical experience. If the actual forfeiture rate is higher than the estimated forfeiture rate, then an adjustment will be made to increase the estimated forfeiture rate, which will result in a decrease to the expense recognized in the Company’s financial statements. If the actual forfeiture rate is lower than the estimated forfeiture rate, then an adjustment will be made to lower the estimated forfeiture rate, which will result in an increase to expense recognized in the Company’s financial statements. The expense the Company recognizes in future periods will be affected by changes in the estimated forfeiture rate and may differ significantly from amounts recognized in the current period.
	Cash proceeds received from the exercise of Stock Options were $2.1 million and $3.6 million for the three and nine months ended September 30, 2014, respectively. There was no income tax benefit realized from the exercise of stock options for the three and nine months ended September 30, 2014. Cash proceeds received from the exercise of Stock Options were $19.2 million and $21.9 million for the three and nine months ended September 30, 2013, respectively. Income tax benefit realized from the exercise of stock options were not material for the three and nine months ended September 30, 2013.
	Valuation Assumptions
	Calculating the fair value of Employee Stock Options requires estimates and significant judgment. The Company uses the Black-Scholes option pricing model to estimate the fair value of its employee stock options, consistent with the provisions of ASC 718, Stock Compensation (“ASC 718”). The fair value of the Stock Options grant is estimated on the date of the grant using the Black-Scholes option pricing model, and is not remeasured as a result of subsequent stock price fluctuations. Options granted to the Company’s independent directors are considered options granted to employees under ASC 718 as defined therein.
	Assumptions used in the Black Scholes valuation model were as follows:
		Independent Directors Options						Independent Directors Options
		Three Months Ended September 30,						Nine Months Ended September 30,
		2014			2013			2014				2013
	Expected term in years	—			—			4				4
	Risk-free interest rate	—			—			1.19		%		0.63		%
	Expected volatility	—			—			44		%		54		%
	Dividend yield	—			—			1.43		%		2.05		%
	Estimated fair value at grant date	—			—			$	5.39			$	4.26
		Employee Stock Options							Employee Stock Options
		Three Months Ended September 30,							Nine Months Ended September 30,
		2014			2013				2014				2013
	Expected term in years	—			4.75				4.75				4.75
	Risk-free interest rate	—			1.28		%		1.58		%		0.99		%
	Expected volatility	—			50		%		45		%		50		%
	Dividend yield	—			1.33		%		1.48		%		1.6		%
	Estimated fair value at grant date	—			$	6.98			$	5.7			$	5.99
	Expected term for the Employee Stock Options and Independent Directors Options is based on the simplified method outlined in ASC 718. In accordance with ASC 718, options are considered to be exercised halfway between the average vesting date and the contractual term of each option grant. The simplified method is applicable for “plain-vanilla” stock options, as defined in ASC 718, only if the Company does not have sufficient historical data upon which to estimate an expected term. Given that the Corporation’s Class A common stock has been publicly traded for less than four years, the Company believes that the simplified method is an applicable methodology to estimate the expected term of the options as of the grant date.
	The risk free interest rates for the Employee Stock Options and Independent Directors Options are based on U.S. Treasury instruments whose terms are consistent with the expected lives of the Stock Options.
	Expected volatility is based on a weighing of the historical and implied volatilities of the Company and for a set of public guideline companies deemed comparable to it. The guideline companies selected operate in a similar industry, pursue similar market opportunities, and are subject to similar risks of the Company. Changes in the subjective assumptions required in the valuation models may significantly affect the estimated value of the Company’s Stock Options, the related stock-based compensation expense and, consequently, its results of operations and comprehensive income.
	The dividend yield is determined based on the Company’s expected dividend payouts.
	The LTIP also provides for other stock based awards (“Other Equity Awards”) which may be granted by the Company’s Executive Compensation Committee (the “Committee”). Pursuant to the terms of the LTIP, the Committee may grant Other Equity Awards that are valued in whole or in part by reference to or that are otherwise based on the fair market value of the Corporation's Class A common stock. The Company did not grant any Other Equity Awards during the three and nine months ended September 30, 2014 or 2013.

Stockholders_Equity

Stockholders' Equity	9 Months Ended
	Sep. 30, 2014
Equity [Abstract]	'
Stockholders' Equity	'
	Stockholders’ Equity
	The following table presents the changes in the corporation's Class A common stock shares outstanding during the nine months ended September 30, 2014, with amounts in thousands:
	Class A Common Stock	As of September 30, 2014
	Balance at January 1, 2014	44,665
	Issued	164
	Exchange of Holding Units into Class A common stock	1,155
	Repurchased	(46	)
	Stock options exercised	267
	Balance at September 30, 2014	46,205
	As of September 30, 2014 and December 31, 2013 there were 34 and 41 shares, respectively, of Class B common stock issued and held by members of Holdings.

Minimum_Net_Capital_Requiremen

Minimum Net Capital Requirements	9 Months Ended
	Sep. 30, 2014
Banking and Thrift [Abstract]	'
Minimum Net Capital Requirements	'
	Minimum Net Capital Requirements
	The tables below present the capital, as defined by the respective regulatory authority, the minimum capital requirement and the excess capital for the Company's regulated entities as of September 30, 2014 and December 31, 2013, with amounts in millions:
		30-Sep-14
		US		HK		UK LTD		Australia		ODL		FSL		FXCMJ		Lucid LLP		Faros
	Capital	$	52.2	$	31.9	$	109.3	$	1.4	$	26.2	$	41.7	$	35.7	$	16.6	$	—
	Minimum capital requirement	30.4		13.5		33		0.9		4.3		6.6		5.2		2.7		—
	Excess capital	$	21.8	$	18.4	$	76.3	$	0.5	$	21.9	$	35.1	$	30.5	$	13.9	$	—
		31-Dec-13
		US		HK		UK LTD		Australia		ODL		FSL		FXCMJ		Lucid LLP		Faros
	Capital	$	64.2	$	33.6	$	86	$	4.7	$	18.4	$	34.8	$	36.3	$	41.8	$	0.1
	Minimum capital requirement	27.1		12.3		24.7		0.4		6.9		8.2		5.6		4.2		—
	Excess capital	$	37.1	$	21.3	$	61.3	$	4.3	$	11.5	$	26.6	$	30.7	$	37.6	$	0.1

Litigation

Litigation	9 Months Ended
	Sep. 30, 2014
Commitments and Contingencies Disclosure [Abstract]	'
Litigation	'
	Litigation
	In the ordinary course of business, we may from time to time be involved in litigation and claims incidental to the conduct of our business, including intellectual property claims. In addition, our business is also subject to extensive regulation, which may result in regulatory proceedings against us. We have also been named in various arbitration and civil litigation cases brought by customers seeking damages for trading losses. However, the arbitrations and litigations are presently in various stages of the judicial process and no judgment can be made regarding the ultimate outcome of the arbitrators’ and/or courts' decisions.
	In 2012, FXCMJ accrued $2.6 million as an estimate to settle certain trading system matters with the Japan Financials Services Agency. The Company settled this matter for $2.3 million during the first quarter of 2013.
	In January 2014, the equity Receiver for a former client of US, Revelation Forex Fund (“Revelation”), its principal, Kevin G. White, and related entities RFF GP, LLC, KGM Capital Management, LLC (collectively “Fund”), filed suit against US, and certain unrelated defendants, in Texas state court. The suit alleges that US is liable under the Texas Securities Act, and the common law: (i) as a “control person;” and, (ii) as an aider and abettor of fraud and a breach of fiduciary obligations; and, (iii) for its negligence. The Receiver seeks joint and several liability for damages in excess of $3.8 million, plus exemplary damages under Texas law, interest, and attorneys’ fees. On February 7, 2014, US filed the equivalent of a motion to dismiss and to compel arbitration based on the mandatory forum selection clause and arbitration agreement in its Client Agreement with the Fund. It also filed an Answer with multiple affirmative defenses. The Trial Court heard argument on US’s motions to dismiss and entered an order denying them without findings of fact or conclusions of law. On March 18, 2014, US filed a Notice of Appeal of the Trial Court's denial of its motion to compel arbitration. On April 16, 2014, US filed a Petition for a Writ of Mandamus to appeal the denial of its motion to dismiss based on the forum selection clause and filed a brief on its appeal seeking to enforce its motion to compel arbitration. Both the Petition and Appeal are pending.
	In February 2014, UK and FSL entered into a settlement with the Financial Conduct Authority ("FCA") following an investigation into trade execution practices of UK and FSL in the period from 2006 to 2010, as well as a breach of notification obligations to the FCA. UK and FSL agreed to pay (a) restitution to affected clients up to $9.9 million; and (b) a financial penalty of GBP 4.0 million (USD 6.6 million), together with any unclaimed restitution. UK and FSL accrued $15.0 million in September 2013, as an estimate to settle this matter recorded in General and administrative expense in the condensed consolidated statements of operations.
	During the three and nine months ended September 30, 2014, the Company accrued an additional $0.7 million and $2.5 million, respectively, of additional restitution, recorded in General and administrative expense in the condensed consolidated statements of operations.
	In April 2014, the Securities and Futures Commission ("SFC") initiated an investigation relating to HK’s past trade execution practices concerning the handling of price improvements in our trading system prior to August 2010. HK continues to comply with information requests from SFC.
	In July 2014, US settled a complaint brought by the National Futures Association (“NFA”) relating to charges of doing business with an unregistered entity and for failing to submit certain trade data reports and was fined $0.2 million. The Commodity Futures Trading Commission (“CFTC”) is also investigating this matter. As of September 30, 2014, the Company accrued $1.0 million related to this matter, recorded in General and administrative expense in the condensed consolidated statements of operations.
	For the outstanding matters referenced above for which a loss is more than remote but less than likely, whether in excess of an accrued liability or where there is no accrued liability, we have estimated a range of possible loss. We believe the estimate of the aggregate range of possible loss in excess of accrued liabilities for such matters is between zero and $4.7 million as of September 30, 2014.
	In view of the inherent difficulty of predicting the outcome of litigation and claims, we cannot predict what the eventual outcome of the pending matters will be, what the timing of the ultimate resolution of these matters will be, or what the eventual loss related to each pending matter may be. Furthermore, the above-referenced matters represented in the estimated aggregate range of possible loss will change from time to time and actual results may vary significantly from the current estimate. An adverse outcome in one or more of these matters could be material to our results of operations or cash flows for any particular reporting period.

Debt

Debt	9 Months Ended
	Sep. 30, 2014
Debt Disclosure [Abstract]	'
Debt	'
	Debt
	Credit Agreement
	On December 19, 2011, Holdings entered into a credit agreement (the “Credit Agreement”) with a syndicate of financial institutions. The Credit Agreement, which matures in 2016, is guaranteed by certain subsidiaries of Holdings and is secured by a pledge of all of the equity interests in certain of Holdings’ domestic subsidiaries and 65% of the voting equity interests in certain of its foreign subsidiaries.
	As of September 30, 2014, Holdings has commitments from lenders for $150.0 million. As of September 30, 2014 and December 31, 2013, Holdings’ outstanding balance under the Credit Agreement was $30.0 million and nil, respectively.
	Under the terms of the Credit Agreement, loans will bear interest at either a Eurodollar Rate or a Base rate (as defined below), at Holdings’ election, plus an applicable margin, based on Holdings’ leverage ratio. In addition, Holdings must pay an annual commitment fee based on Holdings’ leverage ratio on the undrawn commitments under the Credit Agreement. The applicable margin and commitment fees are set forth in the table below:
	Consolidated Leverage Ratio		Commitment Fee			Applicable Margin for Eurodollar Loans		Applicable Margin for Base Rate Loans
	Less than 0.50 to 1.00		0.25	%		1.75	%	0.75	%
	Greater than or equal to 0.50 to 1.00 but less than 1.00 to 1.00		0.3	%		2	%	1	%
	Greater than or equal to 1.00 to 1.00 but less than 1.50 to 1.00		0.35	%		2.25	%	1.25	%
	Greater than or equal to 1.50 to 1.00, but less than 2.00 to 1.00		0.4	%		2.5	%	1.5	%
	Greater than or equal to 2.00 to 1.00		0.45	%		2.75	%	1.75	%
	The Base Rate means for any day a fluctuating rate per annum equal to the highest of (a) the Federal Funds Rate, as defined in the Credit Agreement, plus 0.5%, (b) the rate of interest in effect for such day as publicly announced from time to time by the administrative agent, Bank of America, N.A., as its prime rate, and (c) the Eurodollar Rate plus 1.00%. The
	Eurodollar Rate means the rate per annum equal to (i) the British Bankers Association LIBOR Rate, or (ii) if such rate is not available, the rate per annum determined by the administrative agent.
	Interest expense related to borrowings under the Credit Agreement, including the amortization of debt financing costs, included in Interest on borrowings in the consolidated statements of operations was $0.4 million and $1.2 million for the three and nine months ended September 30, 2014, respectively. Interest expense related to borrowings under the Credit Agreement, including the amortization of debt financing costs, included in Interest on borrowings in the consolidated statements of operations was $0.1 million and $1.3 million for the three and nine months ended September 30, 2013, respectively.
	Pursuant to covenants in the Credit Agreement, Holdings is required to maintain: excess net capital amount of 125% of adjusted net capital required to be maintained as of the last day of any fiscal quarter for US and UK (see Note 12), Consolidated Interest Coverage Ratio, Consolidated Leverage Ratio and Consolidated Senior Leverage Ratio, each as defined in the Credit Agreement, of 4.00 to 1.00, 2.75 to 1.00 and 1.50 to 1.00, respectively, as of the last day of any fiscal quarter, Net Unhedged Exposure, as defined in the Credit Agreement, of less than 20% of total assets of Holdings and its subsidiaries, and Net Unhedged Non-FX Exposure, as defined in the Credit Agreement, of less than 10% of total assets of Holdings and its subsidiaries. In addition, the Credit Agreement contains certain customary covenants as well as certain customary events of default. As of September 30, 2014, Holdings was in compliance with all material covenants.
	During the three and nine months ended September 30, 2014, the weighted average dollar amount of borrowings related to the Credit Agreement were $27.7 million and $37.5 million, respectively, and the weighted average interest rates were 2.90% and 2.68%, respectively. During the three and nine months ended September 30, 2013, the weighted average dollar amount of borrowings related to the Credit Agreement were nil and $46.7 million, respectively, and the weighted average interest rates were nil and 2.44%, respectively.
	Senior Convertible Notes due 2018
	In June 2013, the Corporation issued $172.5 million principal amount of 2.25% Convertible Notes maturing on June 15, 2018 and received net proceeds of $166.5 million, after deducting the initial purchasers' discount and offering expenses. The Convertible Notes pay interest semi-annually on June 15 and December 15 at a rate of 2.25% per year, commencing December 15, 2013. The indenture governing the Convertible Notes does not prohibit the Company from incurring additional senior debt or secured debt, nor does it prohibit any of its subsidiaries from incurring additional liabilities.
	The Convertible Notes will be convertible at an initial conversion rate of 53.2992 shares of the Corporation's Class A common stock per $1,000 principal amount of the Convertible Notes, which is equivalent to an initial conversion price of approximately $18.76. In addition, following certain corporate transactions that occur prior to the maturity date, the Corporation will, in certain circumstances, increase the conversion rate for a holder that elects to convert its Convertible Notes in connection with such corporate transaction. Upon conversion, the Corporation will deliver cash up to the principal amount. With respect to any conversion value in excess of the principal amount, the Corporation will deliver shares of its Class A common stock (unless it elects to deliver cash in lieu of all or a portion of such shares).
	Holders may convert their notes at their option prior to the close of business on the business day immediately preceding March 15, 2018, only under the following circumstances:
	•	during any fiscal quarter commencing after the fiscal quarter ending on September 30, 2013 (and only during such fiscal quarter), if the last reported sale price of the Corporation's Class A common stock for at least 20 trading days (whether or not consecutive) during the period of 30 consecutive trading days ending on the last trading day of the immediately preceding fiscal quarter is greater than or equal to 130% of the applicable conversion price on each applicable trading day;
	•	during the five business day period immediately after any five consecutive trading day period (the “measurement period”) in which the “trading price” (as defined in the offering circular) per $1,000 principal amount of notes for each trading day of such measurement period was less than 98% of the product of the last reported sale price of the Corporation's Class A common stock and the applicable conversion rate on such trading day;
	•	upon the occurrence of specified corporate events; or
	•	on or after March 15, 2018 until the close of business on the second scheduled trading day immediately preceding the maturity date, holders may convert their notes at any time.
	In addition, if the Company undergoes a fundamental change (as defined in the offering circular), holders may, subject to certain conditions, require the Corporation to repurchase their notes for cash at a price equal to 100% of the principal amount of the notes to be purchased, plus accrued and unpaid interest.
	Convertible Note Hedges
	In connection with the offering of the Convertible Notes, the Company entered into privately negotiated convertible note hedge transactions with certain counterparties (the “Convertible Note Hedge Transaction”). The Convertible Note Hedge Transactions will cover, subject to customary anti-dilution adjustments, the number of shares of the Corporation's Class A common stock that will initially underlie the Convertible Notes. Concurrently with entering into the Convertible Note Hedge Transaction, the Company also entered into a separate, privately negotiated warrant transaction (the “Warrant Transaction”) with the same counterparties, whereby the Company sold to the counterparties warrants to purchase, subject to customary anti-dilution adjustments, up to the same number of shares of the Corporation's Class A common stock as in the Convertible Note Hedge Transaction. The strike price of the Warrant Transaction will initially be $21.24 per share of the Corporation's Class A common stock. Subject to certain conditions, the Company may settle the warrants in cash or on a net-share basis.
	The Convertible Note Hedge Transaction and the Warrant Transaction have the effect of increasing the effective conversion price of the Convertible Notes to $21.24 per share. The cost of the Convertible Note Hedge Transaction and the proceeds from the Warrant Transaction was $29.1 million and $18.6 million, respectively. In accordance with Accounting Standards Codification ("ASC") 815, Derivatives and Hedging ("ASC 815"), the Company recorded the cost of the Convertible Note Hedge Transaction and the proceeds from the Warrant Transaction to additional-paid-in-capital in the stockholders' equity in the condensed consolidated statements of financial condition and the recorded values will not be adjusted for subsequent changes in their respective fair values.
	The Convertible Note Hedge Transaction and the Warrant Transaction are separate transactions, in each case, entered into by the Company with certain counterparties, and are not part of the terms of the Convertible Notes and will not affect any holder's right under the Convertible Notes. Holders of the Convertible Notes will not have any rights with respect to the Convertible Hedge Transaction or the Warrant Transaction.
	Under ASC 470, Debt ("ASC 470"), an entity must separately account for the liability and equity components of the convertible debt instruments (such as the Convertible Notes) that may be settled entirely or partially in cash upon conversion in a manner that reflects the issuer's economic interest cost. The effect of ASC 470 on the accounting for the Convertible Notes is that the fair value of the equity component is included in the additional paid-in capital section of stockholders' equity in the Company's condensed consolidated statements of financial condition and the principal amount of the Convertible Notes is reduced by original issue discount to reflect the Convertible Notes fair value at issuance. At issuance, the equity component of the Convertible Notes was valued at $29.1 million and the Convertible Notes were valued at $144.1 million consisting of $172.5 million of principal net of original issuance discount of $29.1 million. The original issue discount will be amortized over the life of the Convertible Notes using the effective interest rate of 6.20%.
	The balances of the liability and equity components as of September 30, 2014, were as follows, with amounts in thousands:
			September 30, 2014
	Liability component - principal		$	172,500
	Deferred bond discount		(22,264		)
	Liability component - net carrying value		$	150,236
	Equity component		$	29,101
	Interest expense related to the Convertible Notes, included in Interest on borrowings in the condensed consolidated statements of operations was as follows, with amounts in thousands:
		Three Months Ended September 30,							Nine Months Ended September 30,
		2014				2013			2014		2013
	Interest expense - stated coupon rate	$	970			$	970		$	2,911	$	1,272
	Interest expense - amortization of deferred bond discount	1,335				1,254			3,932		1,644
	Total interest expense - convertible notes	$	2,305			$	2,224		$	6,843	$	2,916
	The Company incurred $6.0 million of Convertible Notes issuance cost. Amortization of Convertible Notes issuance costs included in Interest on borrowings in the condensed consolidated statements of operations was $0.3 million and $0.9 million for the three and nine months ended September 30, 2014, respectively. Amortization of Convertible Notes issuance costs included in Interest on borrowings in the condensed consolidated statements of operations was $0.3 million and $0.4 million for the three and nine months ended September 30, 2013. Unamortized Convertible Notes issuance cost was $4.4 million and $5.3 million at September 30, 2014 and December 31, 2013, respectively, and is included in Other assets in the condensed consolidated statements of financial condition.
	Notes Payable
	In connection with its Lucid acquisition, the Company issued to the Lucid sellers 3.5% unsecured promissory notes in the amounts of $71.4 million and $15.8 million maturing on December 21, 2012. On December 21, 2012, the Company repaid $64.0 million of these notes and issued a series of 2.25%, $22.9 million unsecured promissory notes for the balance. The notes were pre-paid on June 6, 2013 with a portion of the proceeds received from the Convertible Notes issued on June 3, 2013. In the second quarter of 2013, the Lucid purchase price was increased by $15.3 million due to the final determination of tax balances at the acquisition date adjusted during the measurement period. The Company issued six-month 2.25% unsecured promissory notes to the Lucid sellers for the purchase price increase which matured on December 21, 2013. In satisfaction of the matured notes, the Company repaid $5.5 million and issued a series of 2.25% unsecured promissory notes to the Lucid sellers for the balance of $9.8 million which matured on June 6, 2014. In satisfaction of the matured notes, the Company repaid $2.3 million and issued a series of 2.25% unsecured promissory notes for the balance of $7.5 million which matures on December 6, 2014.

Commitments_and_Contingencies

Commitments and Contingencies	9 Months Ended
	Sep. 30, 2014
Commitments and Contingencies Disclosure [Abstract]	'
Commitments and Contingencies	'
	Commitments and Contingencies
	The Company holds an interest in an inactive entity that formerly provided online FX educational services (“Online Courses”). Online Courses meets the definition of a VIE under ASC 810 and the Company was considered the primary beneficiary. The members who owned the remaining interest in Online Courses had put options to sell their interest to the Company upon a change in control of Holdings. A change in control occurs when the number of Holdings units held by unit holders as of the date of the Online Courses operating agreement, November 17, 2008, cease to make up at least 50% of the voting or vested economic interest securities of Holdings. The change in control occurred during the quarter ended September 30, 2013. Under U.S. GAAP, the value of the put options is recognized upon both the change in control and the exercise of the put options.
	On April 2, 2014 and September 9, 2014, thirty-seven percent and sixty-three percent, respectively, of the put options were exercised and Holdings remitted payments in the amount of $1.3 million and $2.3 million, respectively. Based on the status (inactive and no assets) of Online Courses, the put option payments resulted in a charge to earnings, and General and administrative expense in the condensed consolidated statements of operations for the three and nine months ended September 30, 2014 includes a charge of $2.3 million and $3.6 million, respectively, related to the put option payments.

Exchange_Memberships

Exchange Memberships	9 Months Ended
	Sep. 30, 2014
Brokers and Dealers [Abstract]	'
Exchange Memberships	'
	Exchange Memberships
	The Company’s exchange memberships, which represent ownership interests and shares owned in the Chicago Mercantile and the Intercontinental exchanges and provide the Company with the right to conduct business on the exchanges, are recorded at cost or, if an other than temporary impairment in value has occurred, at a value that reflects management's estimate of the impairment. There were no exchange membership impairments as of September 30, 2014. At September 30, 2014, ownership interests and shares owned with a cost of $2.8 million and $3.7 million, respectively, are included in Other assets in the condensed consolidated statement of financial condition. There were no exchange memberships held at December 31, 2013.

Fair_Value_Measurements

Fair Value Measurements	9 Months Ended
	Sep. 30, 2014
Fair Value Disclosures [Abstract]	'
Fair Value Measurements	'
	Fair Value Measurements
	Fair value is defined as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. Fair value measurement establishes a fair value hierarchy that prioritizes the inputs of valuation techniques used to measure fair value. The hierarchy gives the highest priority to unadjusted quoted prices in active markets for identical assets or liabilities and the lowest priority to unobservable inputs. These three levels of fair value hierarchy are defined as follows:
	Level I:  Quoted prices in active markets for identical assets or liabilities, accessible by the Company at the measurement date.
	Level II:  Quoted prices for similar assets or liabilities in active markets, or quoted prices for identical or similar assets or liabilities in markets that are not active, or other observable inputs other than quoted prices.
	Level III:  Unobservable inputs for assets or liabilities.
	When Level I inputs are available, those inputs are selected for determination of fair value. To value derivatives that are characterized as Level II and III, the Company uses observable inputs for similar assets and liabilities that are available from pricing services or broker quotes. These observable inputs may be supplemented with other methods, including internal models that result in the most representative prices for assets and liabilities with similar characteristics. Multiple inputs may be used to measure fair value, however, the level of fair value for each derivative and financial asset or liability is based on the highest priority level of input within this fair value hierarchy.
	The following tables present the Company's assets and liabilities that are measured at fair value on a recurring basis and the related hierarchy levels, with amounts in thousands:
		Fair Value Measurements on a Recurring Basis
		As of September 30, 2014
		Quoted Prices in Active Markets for Identical Assets (Level I)		Significant Observable Inputs (Level II)		Significant Unobservable Inputs (Level III)			Counterparty and Cash Collateral Netting			Total
	Financial Assets:
	Cash and cash equivalents	$	326,730	$	—	$	—		$	—		$	326,730
	Cash and cash equivalents, held for customers	1,332,399		—		—			—			1,332,399
	Restricted time deposits	—		9,120		—			—			9,120
	Trading securities	633		—		—			—			633
	Due from brokers:
	Exchange traded options	4,049		—		—			—			4,049
	Futures contracts	54,369		—		—			—			54,369
	Netting	—		—		—			(54,614		)	(54,614		)
	Total due from brokers	58,418		—		—			(54,614		)	3,804
	Total assets	$	1,718,180	$	9,120	$	—		$	(54,614	)	$	1,672,686
	Financial Liabilities:
	Customer account liabilities	$	1,332,399	$	—	$	—		$	—		$	1,332,399
	Due to brokers:
	Exchange traded options	7,764		—		—			—			7,764
	Futures contracts	47,060		—		—			—			47,060
	OTC options	—		1,457		—			—			1,457
	Netting	—		—		—			(56,099		)	(54,872		)
	Total due to brokers	54,824		1,457		—			(56,099		)	182
	Securities sold, not yet purchased	3,815		—		—			—			3,815
	Total liabilities	$	1,391,038	$	1,457	$	—		$	(56,099	)	$	1,336,396
		Fair Value Measurements on a Recurring Basis
		As of December 31, 2013
		Quoted Prices in Active Markets for Identical Assets (Level I)		Significant Observable Inputs (Level II)		Significant Unobservable Inputs (Level III)			Counterparty and Cash Collateral Netting			Total
	Financial Assets:
	Cash and cash equivalents	$	365,245	$	—	$	—		$	—		$	365,245
	Cash and cash equivalents, held for customers	1,190,880		—		—			—			1,190,880
	Due from brokers - futures contracts	84		—		—			(84		)	—
	Total assets	$	1,556,209	$	—	$	—		$	(84	)	$	1,556,125
	Financial Liabilities:
	Customer account liabilities	$	1,190,880	$	—	$	—		$	—		$	1,190,880
	Due to brokers - open futures contracts	2,404		—		—			(84		)	2,320
	Follow-on Payment	—		—		3,672			—			3,672
	Total liabilities	$	1,193,284	$	—	$	3,672		$	(84	)	$	1,196,872
	Cash and Cash Equivalents and Cash and Cash Equivalents, held for customers
	Cash and cash equivalents and cash and cash equivalents, held for customers are deemed to be Level I.
	Restricted Time Deposits
	Restricted time deposits consist of pledged time deposits (see Note 4) with original maturities of three months and one year and for which use is contractually restricted. Restricted time deposits are included in Current assets and Non-current assets in the condensed consolidated statements of financial condition, as appropriate. Restricted time deposits are recorded at cost, which approximates fair value and are deemed to be Level II.
	Trading Securities
	Equity securities that the Company purchased with the intent to sell in the near-term are classified as trading securities. These trading securities are reported at their fair value based on the quoted market prices of the securities in active markets and are deemed to be Level I. Changes in fair value of equity securities from trading activity are recorded in Institutional trading revenue in the condensed consolidated statements of operations.
	Due from/to Brokers
	Exchange traded options and open futures contracts, included in Due from and Due to brokers in the condensed consolidated statements of financial condition, are classified as Level I financial assets and liabilities, respectively, as their fair values are based on exchange prices. Over the counter ("OTC") options, included in Due from and Due to brokers in the condensed consolidated statements of financial condition, are valued using market price quotations (where observable) obtained from independent brokers and are classified as Level II financial assets and liabilities.
	Securities Sold, Not Yet Purchased
	Securities sold, not yet purchased, represent the Company’s obligations to deliver the specified security at the contracted price at a future point in time, and thereby create a liability to repurchase the securities in the market at the prevailing prices. The liability for such securities sold short, included in the condensed consolidated statements of financial condition, is marked to market based on the current fair value of the underlying security at the reporting date and is classified as Level I financial liabilities as they are based on exchange prices. Changes in fair value of securities sold, not yet purchased are recorded as unrealized gains or losses in Institutional trading revenue in the condensed consolidated statements of operations. These transactions may involve market risk in excess of the amount currently reflected in the condensed consolidated statements of financial condition.
	The following tables present 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 statements of financial condition, with amounts in thousands:
		As of September 30, 2014				Fair Value Measurements using:
		Carrying Value		Fair Value		Quoted Prices in Active Markets for Identical Assets (Level I)			Significant Observable Inputs (Level II)			Significant Unobservable Inputs (Level III)
	Financial Assets:
	Due from brokers- unsettled spot FX	$	7,980	$	7,980	$	—		$	7,980		$	—
	Due from brokers- unsettled common stock	3,730		3,730		—			3,730			—
	Due from brokers - excess cash collateral	17,446		17,446		—			17,446			—
	Equity method investments	10,405		17,199		—			—			17,199
	Notes receivable	9,608		9,608		—			—			9,608
Exchange memberships	6,429		6,833		—			6,833			—
Total assets	$	55,598	$	62,796	$	—		$	35,989		$	26,807
Financial Liabilities:
Due to brokers- unsettled spot FX	$	734	$	734	$	—		$	734		$	—
Credit agreement	30,000		30,000		—			30,000			—
Notes payable	7,460		7,460		—			—			7,460
Senior convertible notes	150,236		149,909		—			149,909			—
Total liabilities	$	188,430	$	188,103	$	—		$	180,643		$	7,460
	As of December 31, 2013				Fair Value Measurements using:
	Carrying Value		Fair Value		Quoted Prices in Active Markets for Identical Assets (Level I)			Significant Observable Inputs (Level II)			Significant Unobservable Inputs (Level III)
Financial Assets:
Due from brokers- unsettled spot FX	$	5,450	$	5,450	$	—		$	5,450		$	—
Equity method investments	9,793		13,504		—			—			13,504
Notes receivable	11,942		11,942		—			—			11,942
Total assets	$	27,185	$	30,896	$	—		$	5,450		$	25,446
Financial Liabilities:
Due to brokers- unsettled spot FX	$	6,332	$	6,332	$	—		$	6,332		$	—
Notes payable	9,800		9,800		—			—			9,800
Senior convertible notes	146,303		149,418		—			149,418			—
Total liabilities	$	162,435	$	165,550	$	—		$	155,750		$	9,800
Due from/to Brokers - Unsettled Spot FX
Unsettled spot FX, included in Due from brokers and Due to brokers in the condensed consolidated statements of financial condition, are classified as Level II financial assets and liabilities, respectively, and are carried at contracted amounts which approximate fair value based on market price quotations (where observable) obtained from independent brokers.
Due from Brokers - Unsettled Common Stock
The receivable for exchange membership shares sold short, included in Due from brokers in the condensed consolidated statements of financial condition, is classified as a Level II financial asset and is carried at the contracted amount which approximates fair value based on quoted prices.
Due from Brokers - Excess Cash Collateral
Excess cash collateral, included in Due from brokers in the condensed consolidated statements of financial condition, is classified as Level II financial assets.
Equity Method Investments
Equity method investments, included in Other assets in the condensed consolidated statements of financial condition, are classified as Level III financial assets and are carried at cost. The fair value of these investments is based on comparable market multiples and other valuation methods.
Notes Receivable
Notes receivable are carried at contracted amounts which approximate fair value.
Exchange Memberships
Exchange memberships, which include ownership interests and shares owned, are included in Other assets in the condensed consolidated statements of financial condition. Exchange memberships are carried at cost and are classified as Level II financial assets. The fair value is based on quoted prices or recent sales.
Notes Payable
Notes payable, included in the condensed consolidated statements of financial condition, are carried at contracted amounts, which approximate fair value based on the relatively short amount of time until maturity.
Credit Agreement
Balances due under the Credit Agreement are carried at contracted amounts, which approximate fair value based on the short term nature of the borrowing and the variable interest rate.
Senior Convertible Notes
Senior convertible notes are carried at contractual amounts. The fair value of the Senior convertible notes are based on similar recently executed transactions and market price quotations (where observable) obtained from independent brokers.
The following tables reconcile the ending balances of liabilities classified as Level III and identify the total (gains) and losses the Company recognized during the nine months ended September 30, 2014 and twelve months ended December 31, 2013 on such liabilities that were included in the condensed consolidated statements of financial condition as of September 30, 2014 and December 31, 2013, respectively with amounts in thousands:
	As of September 30, 2014
	Beginning Balance		Additions		Net Unrealized / Realized (Gains) Losses			Total
Follow-on Payment	$	3,672	$	—	$	(3,672	)	$	—
Total Level III liabilities	$	3,672	$	—	$	(3,672	)	$	—
	As of December 31, 2013
	Beginning Balance		Additions		Net Unrealized / Realized (Gains) Losses			Total
Follow-on Payment	$	—	$	10,631	$	(6,959	)	$	3,672
Total Level III liabilities	$	—	$	10,631	$	(6,959	)	$	3,672
The Follow-on Payment related to the Faros acquisition was valued using significant unobservable inputs including a multiple of Faros' 2014 EBITDA. The net unrealized/realized (gains)/losses are included in Other income in the condensed consolidated statements of operations.
The Company did not have any transfers in or out of Level I, II and III during the nine months ended September 30, 2014.

Derivative_Financial_Instrumen

Derivative Financial Instruments	9 Months Ended
	Sep. 30, 2014
Derivative Instruments and Hedging Activities Disclosure [Abstract]	'
Derivative Financial Instruments	'
	Derivative Financial Instruments
	Derivative financial instruments are accounted for in accordance with ASC 815 and are included in Due from brokers and Due to brokers in the condensed consolidated statements of financial condition. The Company recognizes all derivative financial instruments in the condensed consolidated statements of financial condition as either assets or liabilities at fair value. The Company has master netting agreements with its respective counterparties under which derivative financial instruments are presented on a net-by counterparty basis in accordance with Topic 210, Balance Sheet (“ASC 210”) and ASC 815. The Company enters into futures contracts to economically hedge the open customer contracts on its CFD business. Futures contracts are exchanged traded contracts to either purchase or sell a specific asset at a specified future date for a specified price. Gains or losses on futures contracts related to the Company's CFD business are included in Retail trading revenue in the condensed consolidated statements of operations. The Company also engages in hedge trading in its electronic market making and institutional foreign exchange spot and futures markets. Gains or losses on hedge trading in the Company's electronic market making and institutional foreign exchange spot and futures markets are included in Institutional trading revenue in the condensed consolidated statements of operations.
	Through its subsidiaries Lucid and V3 (see Note 3), the Company enters into options, futures, forward foreign currency contracts and commodity contracts. Options grant the purchaser, for the payment of a premium, the right to either purchase from or sell to the writer a specified instrument under agreed terms. A forward contract is a commitment to purchase or sell an asset at a future date at a negotiated rate. The Company's derivative transactions held for trading purposes are recorded in Due from/to brokers in the condensed consolidated statements of financial condition. Gains or losses on options, futures and forward contracts held for trading purposes, are included in Institutional trading revenue in the condensed consolidated statements of operations.
	The Company is exposed to risks relating to its derivatives trading positions from the potential inability of counterparties to perform under the terms of the contracts (credit risk) and from changes in the value of the underlying financial instruments (market risk). The Company is subject to credit risk to the extent that any counterparty with which it conducts business with is unable to fulfill its contractual obligations. The Company manages its trading positions by monitoring its positions with and the credit quality of the financial institutions that are party to its derivative trading transactions. Additionally, the Company's netting agreements provide the Company with the right, in the event of a default of the counterparty (such as bankruptcy or a failure to perform), to net a counterparty’s rights and obligations under the agreement and to liquidate and set off collateral against any net amount owed by the counterparty.
	The following tables present the gross and net fair values of the Company derivative transactions and the related offsetting amount permitted under ASC 210 and ASC 815, as of September 30, 2014 and December 31, 2013. Derivative assets and liabilities are net of counterparty and collateral offsets. Collateral offsets include cash margin amounts posted with brokers. Under ASC 210, gross positive fair values are offset against gross negative fair values by counterparty pursuant to enforceable master netting agreements, with amounts in thousands:
		Derivatives Assets
		Included in Due from/to Brokers
		30-Sep-14
		Fair Value			Notional
	Exchange traded options	$	4,049		$	117,046
	Futures contracts	54,369			3,354,098
	Total derivative assets	$	58,418		$	3,471,144
	Netting agreements	(54,614		)
	Total derivative assets	$	3,804
		Derivative Liabilities
		Included in Due from/to Brokers
		30-Sep-14
		Fair Value			Notional
	Exchange traded options	$	7,764		$	100,353
	Futures contracts	47,060			507,547
	OTC options	1,457			1,457
	Total derivative liabilities	$	56,281		$	609,357
	Netting agreements and cash collateral netting	(56,099		)
	Total derivative liabilities	$	182
	Total	$	3,622		$	4,080,501
		Derivatives Assets
		Included in Due from/to Brokers
		December 31, 2013
		Fair Value			Notional
	Futures contracts	$	84		$	19,475
	Netting agreements	(84		)
	Total derivative assets	$	—
		Derivative Liabilities
		Included in Due from/to Brokers
		December 31, 2013
		Fair Value			Notional
	Futures contracts	$	2,404		$	140,429
	Netting agreements	(84		)
	Total derivative liabilities	$	2,320
	Total	$	(2,320	)	$	159,904
	The following table presents the gains (losses) on derivative instruments included in Retail and Institutional trading revenue in the condensed consolidated statements of operations for the three and nine months ended September 30, 2014 and 2013, with amounts in thousands:
		Gains (Losses)
		Three Months ended September 30, 2014									Nine Months ended September 30, 2014
		Retail			Institutional			Total			Retail			Institutional			Total
	Exchange traded options	$	—		$	(5,915	)	$	(5,915	)	$	—		$	14,002		$	14,002
	Futures contracts	(33,031		)	11,850			(21,181		)	(12,227		)	4,799			(7,428		)
	OTC options	—			(777		)	(777		)	—			(394		)	(394		)
	Total	$	(33,031	)	$	5,158		$	(27,873	)	$	(12,227	)	$	18,407		$	6,180
		Gains (Losses)
		Three Months ended September 30, 2013									Nine Months ended September 30, 2013
		Retail			Institutional			Total			Retail			Institutional			Total
	Futures contracts	$	(4,192	)	$	4,547		$	355		$	(13,958	)	$	15,710		$	1,752
	Total	$	(4,192	)	$	4,547		$	355		$	(13,958	)	$	15,710		$	1,752

Income_Taxes

Income Taxes	9 Months Ended
	Sep. 30, 2014
Income Tax Disclosure [Abstract]	'
Income Taxes	'
	Income Taxes
	Holdings operates in the U.S. as a limited liability company that is treated as a partnership for U.S. federal, state and local income tax purposes. As a result, Holdings income from its operations is not subject to U.S. federal income tax because the income is attributable to its members. Accordingly, the Company’s U.S. tax provision is solely based on the portion of Holdings’ income attributable to the Corporation and excludes the income attributable to other members of Holdings whose income is included in Net income (loss) attributable to non-controlling interest in FXCM Holdings, LLC in the condensed consolidated statements of operations.
	In addition to U.S. federal and state income taxes, the Company is subject to Unincorporated Business Tax which is attributable to Holdings' operations apportioned to New York City. The Company’s foreign subsidiaries are also subject to taxes in the jurisdictions in which they operate.
	The Company’s effective tax rate was 29.3% and (182.7)% for the three and nine months ended September 30, 2014, respectively. The Company's effective tax rate was (38.5)% and 36.3% for the three and nine months ended September 30, 2013, respectively. The negative tax rate for the nine months ended September 30, 2014 and the three months ended September 30, 2013 reflects the recording of a tax provision on a book loss. The increase in the effective tax rate for the three months ended September 30, 2014 compared to the three months ended September 30, 2014 was due predominately to recording unfavorable book tax differences for valuation allowances on foreign tax credit carryforwards in 2014, which increases the effective tax rate, compared to recording the effect of the unfavorable adjustments in the prior year on the loss, which decreases the effective tax rate benefit. Additionally, during the three months ended September 30, 2014, the Company elected to treat UK LTD as a controlled foreign corporation for US tax purposes retroactively to January 1, 2014. As a result of this election, the Company is required to recognize from the beginning of the year the value of certain intangible assets, deemed to be transferred to UK LTD, as taxable royalty income. Additionally, a shift in jurisdictional income also affected the rate of tax along with an increase in the Corporation’s ownership of Holdings. The increase in the Corporation’s ownership in Holdings is due to members of Holdings exchanging their units for the Corporation’s Class A common stock and stock awards. The effective tax rate will continue to increase as additional exchanges occur. The decrease in the effective tax rate for the nine months ended September 30, 2014 compared to the nine months ended September, 2013 is due to the Company recording a provision on the loss in the nine months ended September 30, 2014 which resulted from recording a valuation allowance on its foreign tax credits and recognizing the royalty income noted above.
	During the nine months ended September 30, 2014, there were no material changes to the uncertain tax positions.
	The Company is no longer subject to tax examinations by taxing authorities for tax years prior to 2010. During the first quarter of 2014 the Internal Revenue Service concluded an audit of the Company's 2011 federal tax return with no adjustment to the tax owed. The Company presently has no additional open examinations.

Segments

Segments	9 Months Ended
	Sep. 30, 2014
Segment Reporting [Abstract]	'
Segments	'
	Segments
	ASC 280, Segments Reporting, establishes standards for reporting information about operating segments. Operating segments are defined as components of an enterprise about which separate financial information is available that is evaluated regularly by the chief operating decision maker, or decision making group, in deciding how to allocate resources and in assessing performance. The Company’s operations relate to FX trading and related services and operate in two segments — retail and institutional, with different target markets and are covered by a separate sales force, customer support and trading platforms. The Company’s segments are organized around three geographic areas. These geographic areas are the United States, Asia and Europe and are based on the location of its customers’ accounts.
	Retail Trading
	The Company operates its retail business whereby it acts as an agent between retail customers and a collection of large global banks and financial institutions by making foreign currency markets for customers trading in foreign exchange spot markets through its Retail Trading business segment. The Retail Trading business segment includes the Company’s white label relationships, contract for differences, payments for order flow (through August 1, 2014) and rollovers. In addition, the Retail Trading business segment includes offerings to some of the Company’s smaller retail clients to trade with a dealing desk, or principal model.
	Institutional Trading
	Institutional Trading facilitates spot foreign currency trades on behalf of institutional customers, market making and electronic trading in the institutional foreign exchange spot and futures markets. The facilitation of spot foreign currency trades allows customers to obtain the best execution price from external banks and financial institutions.
	Our Institutional Trading segment also includes Lucid, an electronic market marker and trader in the institutional foreign exchange spot and futures markets, and activity from the recent acquisitions of Faros and V3. The V3 acquisition expanded the Lucid business model into a broader array of financial instruments and provides more robust connectivity to various financial exchanges.
	Information concerning the Company’s operations by reportable segment is as follows, with amounts in thousands:
		Three Months Ended September 30, 2014
		Retail Trading			Institutional Trading			Corporate			Total
	Total revenues	$	91,861		$	23,926		$	360		$	116,147
	Total expenses	52,284			27,859			31,724			111,867
	Loss on equity method investments	—			239			137			376
	Income (loss) before income taxes	$	39,577		$	(4,172	)	$	(31,501	)	$	3,904
		Three Months Ended September 30, 2013
		Retail Trading			Institutional Trading			Corporate			Total
	Total revenues	$	90,392		$	22,856		$	—		$	113,248
	Total expenses	56,900			20,721			41,785			119,406
	Loss (gain) on equity method investments	—			244			(61		)	183
	Income (loss) before income taxes	$	33,492		$	1,891		$	(41,724	)	$	(6,341	)
		Nine Months Ended September 30, 2014
		Retail Trading			Institutional Trading			Corporate			Total
	Total revenues	$	252,866		$	75,856		$	360		$	329,082
	Total expenses	156,122			81,049			91,903			329,074
	Loss on equity method investments	—			606			304			910
	Income (loss) before income taxes	$	96,744		$	(5,799	)	$	(91,847	)	$	(902	)
		Nine Months Ended September 30, 2013
		Retail Trading			Institutional Trading			Corporate			Total
	Total revenues	$	294,041		$	82,204		$	—		$	376,245
	Total expenses	166,332			73,636			89,317			329,285
	Loss on equity method investments	—			689			39			728
	Income (loss) before income taxes	$	127,709		$	7,879		$	(89,356	)	$	46,232
	Assets		As of September 30, 2014			As of December 31, 2013
	Retail		$	1,738,368		$	1,622,829
	Institutional		454,887			417,492
	Corporate		191,154			183,626
	Total assets		$	2,384,409		$	2,223,947

Subsequent_Events

Subsequent Events	9 Months Ended
	Sep. 30, 2014
Subsequent Events [Abstract]	'
Subsequent Events	'
	Subsequent Events
	The Company has evaluated our subsequent events through the filing date of this Form 10-Q.
	On November 5, 2014, the Corporation declared a quarterly dividend of $0.06 per share on its outstanding Class A common stock. The dividend is payable on December 31, 2014 to Class A stockholders of record at the close of business on December 19, 2014.

Description_of_Business_and_Ba1

Description of Business and Basis of Presentation (Policies)	9 Months Ended
	Sep. 30, 2014
Accounting Policies [Abstract]	'
Basis of Consolidation	'
	Basis of Consolidation
	The accompanying condensed consolidated financial statements are presented in accordance with accounting principles generally accepted in the United States of America (“U.S. GAAP”). The Company consolidates those entities in which it is the primary beneficiary of a variable-interest entity ("VIE") as required by Financial Accounting Standards Board (“FASB”) Accounting Standards Codification Topic (“ASC”) 810, Consolidations (“ASC 810”), or entities where it has a controlling interest. Intercompany accounts and transactions are eliminated in consolidation.
	As indicated above, the Corporation operates and controls all of the businesses and affairs of Holdings and its subsidiaries. As such, the Corporation consolidates the financial results of Holdings and records a non-controlling interest for the economic interest in Holdings not owned by the Corporation. The Corporation’s and the non-controlling unit holders’ economic interest in Holdings was 56.4% and 43.6%, respectively, as of September 30, 2014. The Corporation’s and the non-controlling unit holders’ economic interest in Holdings was 54.8% and 45.2%, respectively, as of December 31, 2013.
	Net income attributable to the non-controlling interest in Holdings in the condensed consolidated statements of operations represents the portion of earnings or loss attributable to the economic interest in Holdings held by the non-controlling unit holders. Net income attributable to other non-controlling interests in the condensed consolidated statements of operations represents the portion of net income or loss attributable to the non-controlling interests of Lucid Markets Trading Limited ("Lucid"), Faros Trading LLC ("Faros"), V3 Markets, LLC ("V3") (see Note 3) and other consolidated entities. Net income attributable to the non-controlling interest in Lucid represents the portion of earnings or loss attributable to the 49.9% economic interest held by Lucid non-controlling members whose allocation among the non-controlling members is not contingent upon services being provided. The portion of the 49.9% of Lucid earnings allocated among the non-controlling members of Lucid contingent on services provided is reported as a component of compensation expense under Allocation of net income to Lucid members for services provided in the condensed consolidated statements of operations. Net income or loss attributable to the non-controlling interests in Faros and V3 represent the portion of earnings or loss attributable to the 49.9% economic interest held by Faros and V3 non-controlling members. Net income or loss attributable to the non-controlling interests in other consolidated entities represents the portion of earnings or loss attributable to the economic interests held by the non-controlling members.
	Non-controlling interests in the condensed consolidated statements of financial condition represents the portion of equity attributable to the non-controlling interests of Holdings, Lucid, Faros, V3 and other consolidated entities. The allocation of equity to non-controlling interests is based on the percentage owned by the non-controlling interest in the respective entity.
	The Company’s condensed consolidated financial statements include the following significant subsidiaries of Holdings:
	Forex Capital Markets L.L.C.	(“US”)
	FXCM Asia Limited	(“HK”)
	Forex Capital Markets Limited	(“UK LTD”)
	FXCM Australia Limited	(“Australia”)
	ODL Group Limited	(“ODL”)
	FXCM Securities Limited	(“FSL”)
	FXCM Japan Securities Co., Ltd.	(“FXCMJ”)
	FXCM UK Merger Limited	(“Merger”)
	Lucid Markets Trading Limited	(“Lucid”)
	Lucid Markets LLP	("Lucid LLP")
	Faros Trading LLC	("Faros")
	V3 Markets, LLC	("V3")
	Investments where the Company is deemed to exercise significant influence, but no control, are accounted for using the equity method of accounting. The Company records its pro-rata share of earnings or losses each period and records any dividends as a reduction in the investment balance. The carrying value of these investments are included in Other assets in the condensed consolidated statements of financial condition and earnings or losses are included in Loss on equity method investments, net in the condensed consolidated statements of operations.
Use of Estimates	'
	Use of Estimates
	The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the condensed consolidated financial statements as well as the reported amount of revenue and expenses during the year. Actual results could differ from those estimates and could have a material impact on the consolidated financial statements.
Reclassifications	'
	Reclassifications
	Certain reclassifications have been made to previously reported amounts to conform to the current presentation.
Accounting Pronouncement Adopted in 2014	'
	Accounting Pronouncement Adopted in 2014
	Obligations Resulting from Joint and Several Liability Arrangements
	In February 2013, the FASB issued Accounting Standards Update ("ASU") No. 2013-04, Obligations Resulting from Joint and Several Liability Arrangements for Which the Total Amount of the Obligation is Fixed at the Reporting Date. This standard requires an entity to measure obligations resulting from joint and several liability arrangements for which the total amount of the obligation is fixed at the reporting date as the sum of (i) the amount the entity agreed to pay on the basis of its arrangement among its co-obligors and (ii) any additional amount it expect to pay on behalf of its co-obligors.
	This guidance became effective for the Company on January 1, 2014 and did not have a material impact on the presentation of the Company’s unaudited condensed consolidated financial statements.
	Parent's Accounting for the Cumulative Translation Adjustment upon Derecognition of an Investment within a Foreign Entity or of an Investment in a Foreign Entity
	In March 2013, the FASB issued ASU No. 2013-05, Parent's Accounting for the Cumulative Translation Adjustment upon Derecognition of Certain Subsidiaries or Groups of Assets within a Foreign Entity or of an Investment in Foreign Entity. This standard addresses whether consolidation guidance or foreign currency guidance applies to the release of the cumulative translation adjustment into net income when a parent sells all or a part of its investment in a foreign entity or no longer holds a controlling financial interest in a subsidiary or net assets that are a business (other than a sale of in-substance real estate) within a foreign entity. The standard also resolves the diversity in practice for the cumulative translation adjustment treatment in business combinations achieved in stages involving foreign entities.
	Under this standard, the entire amount of the cumulative translation adjustment associated with the foreign entity should be released into earnings when there has been: (i) a sale of a subsidiary or group of net assets within a foreign entity and the sale represents a complete or substantially complete liquidation of the foreign entity in which the subsidiary or the net assets had resided; (ii) a loss of a controlling financial interest in an investment in a foreign entity; or (iii) a change in accounting method from applying the equity method to an investment in a foreign entity to consolidating the foreign entity.
	This guidance became effective for the Company on January 1, 2014 and did not have a material impact on the presentation of the Company’s unaudited condensed consolidated financial statements.
	Presentation of Unrecognized Tax Benefits
	In July 2013, the FASB issued ASU No. 2013-11, Presentation of Unrecognized Tax Benefits When a Net Operating Loss Carryforward, a Similar Tax Loss, or a Tax Credit Carryforward Exists. This standard requires a liability related to unrecognized tax benefits to be presented as a reduction to the related deferred tax asset for a net operating loss carryforward or a tax credit carryforward. When the carryforwards are not available at the reporting date under the tax law of the applicable jurisdiction or the tax law of the applicable jurisdiction does not require, and the entity does not intend to use, the deferred tax asset for such purpose, the unrecognized tax benefit will be presented in the financial statements as a liability and will not be combined with the related deferred tax asset.
	This guidance became effective for the Company on January 1, 2014 and did not have a material impact on the presentation of the Company’s unaudited condensed consolidated financial statements.
	Recently Issued Accounting Pronouncements
	Reporting Discontinued Operations
	In April 2014, the FASB issued ASU No. 2014-08, Presentation of Financial Statements (Topic 205) and Property, Plant, and Equipment (Topic 360): Reporting Discontinued Operations and Disclosures of Disposals of Components of an Entity. Under this standard, a discontinued operation will include a disposal of a major part of an entity’s operations and financial results such as a separate major line of business or a separate major geographical area of operations. The standard also raises the threshold to be a major operation but no longer precludes discontinued operations presentation where there is significant continuing involvement or cash flows with a disposed component of an entity. The standard expands disclosures to include cash flows where there is significant continuing involvement with a discontinued operation and the pre-tax profit or loss of disposal transactions not reported as discontinued operations. The standard is effective prospectively for years beginning on or after December 15, 2014, with early application permitted. The Company plans to adopt the standard prospectively on its required effective date of January 1, 2015 and the impact, if any, on the Company’s consolidated financial condition, results of operations or cash flows will be dependent on the nature of future disposals.
	Revenue from Contracts with Customers
	In May 2014, the FASB issued ASU No. 2014-09, Revenue from Contracts with Customers. The standard states that an entity should recognize revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. The standard sets out the following five steps an entity should apply to achieve this core principle.
	•Identify the contract(s) with a customer.
	•Identify the performance obligations in the contract.
	•Determine the transaction price.
	•Allocate the transaction price to the performance obligations in the contract.
	•Recognize revenue when (or as) the entity satisfies a performance obligation.
	For a public entity, the standard is effective for annual reporting periods beginning after December 15, 2016, including interim periods within that reporting period. Early application is not permitted. The Company is currently evaluating the impact this standard will have on its consolidated financial condition, results of operations, cash flows and disclosures and is currently unable to estimate the impact of adopting this guidance.

Description_of_Business_and_Ba2

Description of Business and Basis of Presentation (Tables)	9 Months Ended
	Sep. 30, 2014
Accounting Policies [Abstract]	'
Schedule of Significant Subsidiaries	'
	The Company’s condensed consolidated financial statements include the following significant subsidiaries of Holdings:
	Forex Capital Markets L.L.C.	(“US”)
	FXCM Asia Limited	(“HK”)
	Forex Capital Markets Limited	(“UK LTD”)
	FXCM Australia Limited	(“Australia”)
	ODL Group Limited	(“ODL”)
	FXCM Securities Limited	(“FSL”)
	FXCM Japan Securities Co., Ltd.	(“FXCMJ”)
	FXCM UK Merger Limited	(“Merger”)
	Lucid Markets Trading Limited	(“Lucid”)
	Lucid Markets LLP	("Lucid LLP")
	Faros Trading LLC	("Faros")
	V3 Markets, LLC	("V3")

Holdings_Tables

Holdings (Tables)	9 Months Ended
	Sep. 30, 2014
Noncontrolling Interest [Abstract]	'
Corporation's interests in Holdings	'
	Changes in the non-controlling and the Corporation’s interests in Holdings for the nine months ended September 30, 2014 are presented in the following table:
		Controlling Units		Non-Controlling Units		Total Units		FXCM Inc.		Non-Controlling		Total
	Balance as of January 1, 2014	44,664,884		36,835,821		81,500,705		54.8	%	45.2	%	100	%
	Holdings units acquired by FXCM Inc. related to exchanges of Holdings units for shares of Class A common stock	1,155,359		(1,155,359	)	—		1.4	%	(1.4	)%	—	%
	Holding units repurchased related to Class A common stock repurchased	(45,985	)	—		(45,985	)	—	%	—	%	—	%
	Exercise of stock options	266,500		—		266,500		0.1	%	(0.1	)%	—	%
	Issuance under equity based compensation	163,832		—		163,832		0.1	%	(0.1	)%	—	%
	Balance as of September 30, 2014	46,204,590		35,680,462		81,885,052		56.4	%	43.6	%	100	%

Business_Acquisition_Tables

Business Acquisition (Tables)	9 Months Ended
	Sep. 30, 2014
Business Acquisition [Line Items]	'
Business Acquisition, Pro Forma Information	'
	The Company's pro forma condensed combined financial information for the acquisitions completed in 2014 (i.e. V3), and 2013 (i.e., Faros) are presented as they may have appeared if all acquisitions had been completed on January 1, 2014 and 2013, with amounts in thousands:
		Three Months Ended September 30,						Nine Months Ended September 30,
		2014			2013			2014			2013
	Total revenue	$	116,147		$	124,181		$	329,082		$	416,843
	Net income (loss) before non-controlling interest	$	2,760		$	(9,249	)	$	(4,615	)	$	33,856
V3	'
Business Acquisition [Line Items]	'
Schedule of Recognized Identified Assets Acquired and Liabilities Assumed	'
	The following condensed statement of net assets acquired reflects the amounts of V3 net assets recognized as of the V3 Acquisition Date, with amounts in thousands:
		As of January 21, 2014
	Assets
	Office, communication and computer equipment, net	$	973
	Intangible assets	2,020
	Exchange memberships and common equity shares	6,429
	Equity method investments, net	1,523
	Other assets	1,392
	Total assets	$	12,337
	Liabilities	(107		)
	Fair value of net assets acquired	$	12,230
	V3 Purchase Price Allocation (¹)
	(Amounts in thousands)
	Purchase price				$	15,825
	Non-Controlling interest				15,762
	Total fair value at Acquisition Date				31,587
	Net assets acquired	$	10,210
	Adjustments to reflect acquired assets and liabilities at fair value
	Trading platform (2)	950
	Processing platform (3)	150
	Non-compete agreement (4)	450
	Executory contract (5)	470
	Fair value of net assets acquired				12,230
	Goodwill resulting from the V3 acquisition				$	19,357
	__________________
		(1)	The amounts included in the V3 Purchase Price Allocation table represent the allocation of the purchase price and includes revisions made during the 12 month remeasurement period from the V3 Acquisition Date.
		(2)	Consists of internally developed software platforms that support trade execution, with an amortization life of 4 years.
		(3)	Consists of an internally developed software platform that supports trading, with an amortization life of 5 years.
		(4)	Amortization life is 1 year.
		(5)	Consists of a service agreement relating to fiber optics, wireless and other services, with an amortization life of 3 years.
Business Acquisition, Pro Forma Information	'
	The following condensed financial information presents the resulting operations of V3 from the V3 Acquisition Date to September 30, 2014, with amounts in thousands:
		For the period
		January 21, 2014 to
		30-Sep-14
	Total revenue	$	14,384
	Net loss	$	(2,052	)
Faros	'
Business Acquisition [Line Items]	'
Schedule of Recognized Identified Assets Acquired and Liabilities Assumed	'
	Faros Purchase Price Allocation
	(Amounts in thousands)
	Purchase price				$	15,631
	Non-Controlling interest				15,569
	Total fair value at Acquisition Date				31,200
	Net assets acquired	$	137
	Adjustments to reflect acquired assets and liabilities at fair value
	Customer relationships (1)	6,000
	Non-compete agreement (2)	1,900
	Trade name (3)	130
	Fair value of net assets acquired				8,167
	Goodwill resulting from the Faros acquisition				$	23,033
	__________________
	(1)	Consists of institutional and bank customers, with an amortization life of 4 years.
	(2)	Amortization life is 9 years.
	(3)	Amortization life is 3 year.
	The following condensed statement of net assets acquired reflects the amounts of Faros net assets recognized as of the Faros Acquisition Date, with amounts in thousands:
		As of September 20, 2013
	Assets
	Cash and cash equivalents	$	1,055
	Accounts receivable, net	40
	Office, communication and computer equipment, net	31
	Intangible assets	8,030
	Other assets	76
	Total assets	$	9,232
	Liabilities
	Accounts payable and accrued expenses	$	1,065
	Total liabilities	$	1,065
	Fair value of net assets acquired	$	8,167

Accounts_Receivable_and_Other_1

Accounts Receivable and Other Receivables (Tables)	9 Months Ended
	Sep. 30, 2014
Receivables [Abstract]	'
Schedule of Accounts Recievable and Other Receivable	'
	Accounts and other receivables consisted of the following:
		September 30, 2014	December 31, 2013
	Accounts receivable, net	11,323	9,953
	Notes receivable	—	5,992
	Tax receivable	9,021	3,861
	Total accounts and other receivables	20,344	19,806

Earnings_per_Share_Tables

Earnings per Share (Tables)	9 Months Ended
	Sep. 30, 2014
Earnings Per Share [Abstract]	'
Reconciliation of Numerator and Denominator Used in Basic and Diluted EPS Calculations	'
	The following is a reconciliation of the numerator and denominator used in the basic and diluted EPS calculations, with amounts in thousands except per share data:
		Three Months Ended September 30,					Nine Months Ended September 30,
		2014		2013			2014		2013
	Basic and diluted net income (loss) per share:
	Numerator
	Net income (loss) available to holders of Class A common stock	$	2,392	$	(5,122	)	$	1,391	$	11,862
	Earnings allocated to participating securities	—		—			—		—
	Earnings available for common stockholders	$	2,392	$	(5,122	)	$	1,391	$	11,862
	Denominator for basic net income per share of Class A common stock
	Weighted average shares of Class A common stock	42,963		33,718			40,108		30,983
	Add dilutive effect of the following:
	Weighted average of Lucid's first anniversary shares issued on June 18, 2013	—		—			—		738
	Weighted average of Lucid's second anniversary shares issued on June 18, 2014	—		—			1,381		—
	Stock options	856		751			878		288
	Convertible note hedges	—		—			—		—
	Warrants	—		—			—		—
	Dilutive weighted average shares of Class A common stock	43,819		34,469			42,367		32,009
	Basic income (loss) per share of Class A common stock	$	0.06	$	(0.15	)	$	0.03	$	0.38
	Diluted income (loss) per share of Class A common stock	$	0.05	$	(0.15	)	$	0.03	$	0.37

Related_Party_Transactions_Tab

Related Party Transactions (Tables)	9 Months Ended
	Sep. 30, 2014
Related Party Transactions [Abstract]	'
Amounts Receivable From, And Payable To, Related Parties	'
	Amounts receivable from, and payable to, related parties are set forth below, with amounts in thousands:
		30-Sep-14		December 31, 2013
	Receivables
	Advances to Holdings non-controlling members	$	305	$	940
	Accounts receivable - Lucid non-controlling members	968		—
	Notes receivable and interest - Lucid non-controlling members	8,203		—
	Advances to employees	720		826
		$	10,196	$	1,766
	Payables
	Guarantee agreement ("Monetary Guaranty")	$	6,561	$	8,363
	Employees	1,797		708
	Shareholders with greater than 5% ownership in the Company	—		200
	Due to Lucid non-controlling members in connection with the allocation of net income to Lucid non-controlling members for services provided	7,159		9,826
	Due to Lucid non-controlling members in connection with trade settlements	—		169
	Notes payable to Lucid non-controlling members in connection with the acquisition	7,460		9,800
	Tax receivable agreement	151,838		150,257
	Follow-on Payment	—		3,672
		$	174,815	$	182,995

StockBased_Compensation_Tables

Stock-Based Compensation (Tables)	9 Months Ended
	Sep. 30, 2014
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]	'
Schedule of Share-based Compensation, Stock Options, Activity	'
	The following table summarizes the Company’s stock options activity as of September 30, 2014 and changes for the nine months then ended:
	Options		Shares			Weighted-				Weighted-
						Average Exercise Price				Average Remaining Contractual Term
	Outstanding at January 1, 2014		7,607,800			$	13.48			4.3
	Granted		648,490			$	16.28
	Exercised		(266,500	)		$	13.54
	Forfeited or expired		(209,900	)		$	13.1
	Outstanding as of September 30, 2014		7,779,890			$	13.72			3.81
	Vested or expected to vest at September 30, 2014		7,704,862			$	13.73			3.81
	Exercisable as of September 30, 2014		4,632,150			$	13.52			3.43
Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions	'
	Assumptions used in the Black Scholes valuation model were as follows:
		Independent Directors Options						Independent Directors Options
		Three Months Ended September 30,						Nine Months Ended September 30,
		2014			2013			2014				2013
	Expected term in years	—			—			4				4
	Risk-free interest rate	—			—			1.19		%		0.63		%
	Expected volatility	—			—			44		%		54		%
	Dividend yield	—			—			1.43		%		2.05		%
	Estimated fair value at grant date	—			—			$	5.39			$	4.26
		Employee Stock Options							Employee Stock Options
		Three Months Ended September 30,							Nine Months Ended September 30,
		2014			2013				2014				2013
	Expected term in years	—			4.75				4.75				4.75
	Risk-free interest rate	—			1.28		%		1.58		%		0.99		%
	Expected volatility	—			50		%		45		%		50		%
	Dividend yield	—			1.33		%		1.48		%		1.6		%
	Estimated fair value at grant date	—			$	6.98			$	5.7			$	5.99

Stockholders_Equity_Tables

Stockholders' Equity (Tables)	9 Months Ended
	Sep. 30, 2014
Equity [Abstract]	'
Schedule of Stockholders Equity	'
	The following table presents the changes in the corporation's Class A common stock shares outstanding during the nine months ended September 30, 2014, with amounts in thousands:
	Class A Common Stock	As of September 30, 2014
	Balance at January 1, 2014	44,665
	Issued	164
	Exchange of Holding Units into Class A common stock	1,155
	Repurchased	(46	)
	Stock options exercised	267
	Balance at September 30, 2014	46,205

Minimum_Net_Capital_Requiremen1

Minimum Net Capital Requirements (Tables)	9 Months Ended
	Sep. 30, 2014
Banking and Thrift [Abstract]	'
Minimum Capital Requirement And the Excess Capital	'
	The tables below present the capital, as defined by the respective regulatory authority, the minimum capital requirement and the excess capital for the Company's regulated entities as of September 30, 2014 and December 31, 2013, with amounts in millions:
		30-Sep-14
		US		HK		UK LTD		Australia		ODL		FSL		FXCMJ		Lucid LLP		Faros
	Capital	$	52.2	$	31.9	$	109.3	$	1.4	$	26.2	$	41.7	$	35.7	$	16.6	$	—
	Minimum capital requirement	30.4		13.5		33		0.9		4.3		6.6		5.2		2.7		—
	Excess capital	$	21.8	$	18.4	$	76.3	$	0.5	$	21.9	$	35.1	$	30.5	$	13.9	$	—
		31-Dec-13
		US		HK		UK LTD		Australia		ODL		FSL		FXCMJ		Lucid LLP		Faros
	Capital	$	64.2	$	33.6	$	86	$	4.7	$	18.4	$	34.8	$	36.3	$	41.8	$	0.1
	Minimum capital requirement	27.1		12.3		24.7		0.4		6.9		8.2		5.6		4.2		—
	Excess capital	$	37.1	$	21.3	$	61.3	$	4.3	$	11.5	$	26.6	$	30.7	$	37.6	$	0.1

Debt_Tables

Debt (Tables)	9 Months Ended
	Sep. 30, 2014
Debt Disclosure [Abstract]	'
Schedule Of Applicable Margin and Commitment Fees	'
	The applicable margin and commitment fees are set forth in the table below:
	Consolidated Leverage Ratio		Commitment Fee			Applicable Margin for Eurodollar Loans		Applicable Margin for Base Rate Loans
	Less than 0.50 to 1.00		0.25	%		1.75	%	0.75	%
	Greater than or equal to 0.50 to 1.00 but less than 1.00 to 1.00		0.3	%		2	%	1	%
	Greater than or equal to 1.00 to 1.00 but less than 1.50 to 1.00		0.35	%		2.25	%	1.25	%
	Greater than or equal to 1.50 to 1.00, but less than 2.00 to 1.00		0.4	%		2.5	%	1.5	%
	Greater than or equal to 2.00 to 1.00		0.45	%		2.75	%	1.75	%
Convertible Debt	'
	The balances of the liability and equity components as of September 30, 2014, were as follows, with amounts in thousands:
			September 30, 2014
	Liability component - principal		$	172,500
	Deferred bond discount		(22,264		)
	Liability component - net carrying value		$	150,236
	Equity component		$	29,101
	Interest expense related to the Convertible Notes, included in Interest on borrowings in the condensed consolidated statements of operations was as follows, with amounts in thousands:
		Three Months Ended September 30,							Nine Months Ended September 30,
		2014				2013			2014		2013
	Interest expense - stated coupon rate	$	970			$	970		$	2,911	$	1,272
	Interest expense - amortization of deferred bond discount	1,335				1,254			3,932		1,644
	Total interest expense - convertible notes	$	2,305			$	2,224		$	6,843	$	2,916

Fair_Value_Measurements_Tables

Fair Value Measurements (Tables)	9 Months Ended
	Sep. 30, 2014
Fair Value Disclosures [Abstract]	'
Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis	'
	The following tables present the Company's assets and liabilities that are measured at fair value on a recurring basis and the related hierarchy levels, with amounts in thousands:
		Fair Value Measurements on a Recurring Basis
		As of September 30, 2014
		Quoted Prices in Active Markets for Identical Assets (Level I)		Significant Observable Inputs (Level II)		Significant Unobservable Inputs (Level III)			Counterparty and Cash Collateral Netting			Total
	Financial Assets:
	Cash and cash equivalents	$	326,730	$	—	$	—		$	—		$	326,730
	Cash and cash equivalents, held for customers	1,332,399		—		—			—			1,332,399
	Restricted time deposits	—		9,120		—			—			9,120
	Trading securities	633		—		—			—			633
	Due from brokers:
	Exchange traded options	4,049		—		—			—			4,049
	Futures contracts	54,369		—		—			—			54,369
	Netting	—		—		—			(54,614		)	(54,614		)
	Total due from brokers	58,418		—		—			(54,614		)	3,804
	Total assets	$	1,718,180	$	9,120	$	—		$	(54,614	)	$	1,672,686
	Financial Liabilities:
	Customer account liabilities	$	1,332,399	$	—	$	—		$	—		$	1,332,399
	Due to brokers:
	Exchange traded options	7,764		—		—			—			7,764
	Futures contracts	47,060		—		—			—			47,060
	OTC options	—		1,457		—			—			1,457
	Netting	—		—		—			(56,099		)	(54,872		)
	Total due to brokers	54,824		1,457		—			(56,099		)	182
	Securities sold, not yet purchased	3,815		—		—			—			3,815
	Total liabilities	$	1,391,038	$	1,457	$	—		$	(56,099	)	$	1,336,396
		Fair Value Measurements on a Recurring Basis
		As of December 31, 2013
		Quoted Prices in Active Markets for Identical Assets (Level I)		Significant Observable Inputs (Level II)		Significant Unobservable Inputs (Level III)			Counterparty and Cash Collateral Netting			Total
	Financial Assets:
	Cash and cash equivalents	$	365,245	$	—	$	—		$	—		$	365,245
	Cash and cash equivalents, held for customers	1,190,880		—		—			—			1,190,880
	Due from brokers - futures contracts	84		—		—			(84		)	—
	Total assets	$	1,556,209	$	—	$	—		$	(84	)	$	1,556,125
	Financial Liabilities:
	Customer account liabilities	$	1,190,880	$	—	$	—		$	—		$	1,190,880
	Due to brokers - open futures contracts	2,404		—		—			(84		)	2,320
	Follow-on Payment	—		—		3,672			—			3,672
	Total liabilities	$	1,193,284	$	—	$	3,672		$	(84	)	$	1,196,872
Fair Value, by Balance Sheet Grouping	'
	The following tables present 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 statements of financial condition, with amounts in thousands:
		As of September 30, 2014				Fair Value Measurements using:
		Carrying Value		Fair Value		Quoted Prices in Active Markets for Identical Assets (Level I)			Significant Observable Inputs (Level II)			Significant Unobservable Inputs (Level III)
	Financial Assets:
	Due from brokers- unsettled spot FX	$	7,980	$	7,980	$	—		$	7,980		$	—
	Due from brokers- unsettled common stock	3,730		3,730		—			3,730			—
	Due from brokers - excess cash collateral	17,446		17,446		—			17,446			—
	Equity method investments	10,405		17,199		—			—			17,199
	Notes receivable	9,608		9,608		—			—			9,608
	Exchange memberships	6,429		6,833		—			6,833			—
	Total assets	$	55,598	$	62,796	$	—		$	35,989		$	26,807
	Financial Liabilities:
	Due to brokers- unsettled spot FX	$	734	$	734	$	—		$	734		$	—
	Credit agreement	30,000		30,000		—			30,000			—
	Notes payable	7,460		7,460		—			—			7,460
	Senior convertible notes	150,236		149,909		—			149,909			—
	Total liabilities	$	188,430	$	188,103	$	—		$	180,643		$	7,460
		As of December 31, 2013				Fair Value Measurements using:
		Carrying Value		Fair Value		Quoted Prices in Active Markets for Identical Assets (Level I)			Significant Observable Inputs (Level II)			Significant Unobservable Inputs (Level III)
	Financial Assets:
	Due from brokers- unsettled spot FX	$	5,450	$	5,450	$	—		$	5,450		$	—
	Equity method investments	9,793		13,504		—			—			13,504
	Notes receivable	11,942		11,942		—			—			11,942
	Total assets	$	27,185	$	30,896	$	—		$	5,450		$	25,446
	Financial Liabilities:
	Due to brokers- unsettled spot FX	$	6,332	$	6,332	$	—		$	6,332		$	—
	Notes payable	9,800		9,800		—			—			9,800
	Senior convertible notes	146,303		149,418		—			149,418			—
	Total liabilities	$	162,435	$	165,550	$	—		$	155,750		$	9,800
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation	'
	The following tables reconcile the ending balances of liabilities classified as Level III and identify the total (gains) and losses the Company recognized during the nine months ended September 30, 2014 and twelve months ended December 31, 2013 on such liabilities that were included in the condensed consolidated statements of financial condition as of September 30, 2014 and December 31, 2013, respectively with amounts in thousands:
		As of September 30, 2014
		Beginning Balance		Additions		Net Unrealized / Realized (Gains) Losses			Total
	Follow-on Payment	$	3,672	$	—	$	(3,672	)	$	—
	Total Level III liabilities	$	3,672	$	—	$	(3,672	)	$	—
		As of December 31, 2013
		Beginning Balance		Additions		Net Unrealized / Realized (Gains) Losses			Total
	Follow-on Payment	$	—	$	10,631	$	(6,959	)	$	3,672
	Total Level III liabilities	$	—	$	10,631	$	(6,959	)	$	3,672

Derivative_Financial_Instrumen1

Derivative Financial Instruments (Tables)	9 Months Ended
	Sep. 30, 2014
Derivative Instruments and Hedging Activities Disclosure [Abstract]	'
Gross and Net Fair Values of Company Derivative Transactions and Related Offsetting Amount Permitted	'
	The following tables present the gross and net fair values of the Company derivative transactions and the related offsetting amount permitted under ASC 210 and ASC 815, as of September 30, 2014 and December 31, 2013. Derivative assets and liabilities are net of counterparty and collateral offsets. Collateral offsets include cash margin amounts posted with brokers. Under ASC 210, gross positive fair values are offset against gross negative fair values by counterparty pursuant to enforceable master netting agreements, with amounts in thousands:
		Derivatives Assets
		Included in Due from/to Brokers
		30-Sep-14
		Fair Value			Notional
	Exchange traded options	$	4,049		$	117,046
	Futures contracts	54,369			3,354,098
	Total derivative assets	$	58,418		$	3,471,144
	Netting agreements	(54,614		)
	Total derivative assets	$	3,804
		Derivative Liabilities
		Included in Due from/to Brokers
		30-Sep-14
		Fair Value			Notional
	Exchange traded options	$	7,764		$	100,353
	Futures contracts	47,060			507,547
	OTC options	1,457			1,457
	Total derivative liabilities	$	56,281		$	609,357
	Netting agreements and cash collateral netting	(56,099		)
	Total derivative liabilities	$	182
	Total	$	3,622		$	4,080,501
		Derivatives Assets
		Included in Due from/to Brokers
		December 31, 2013
		Fair Value			Notional
	Futures contracts	$	84		$	19,475
	Netting agreements	(84		)
	Total derivative assets	$	—
		Derivative Liabilities
		Included in Due from/to Brokers
		December 31, 2013
		Fair Value			Notional
	Futures contracts	$	2,404		$	140,429
	Netting agreements	(84		)
	Total derivative liabilities	$	2,320
	Total	$	(2,320	)	$	159,904
Derivative Instruments, Gain (Loss)	'
	The following table presents the gains (losses) on derivative instruments included in Retail and Institutional trading revenue in the condensed consolidated statements of operations for the three and nine months ended September 30, 2014 and 2013, with amounts in thousands:
		Gains (Losses)
		Three Months ended September 30, 2014									Nine Months ended September 30, 2014
		Retail			Institutional			Total			Retail			Institutional			Total
	Exchange traded options	$	—		$	(5,915	)	$	(5,915	)	$	—		$	14,002		$	14,002
	Futures contracts	(33,031		)	11,850			(21,181		)	(12,227		)	4,799			(7,428		)
	OTC options	—			(777		)	(777		)	—			(394		)	(394		)
	Total	$	(33,031	)	$	5,158		$	(27,873	)	$	(12,227	)	$	18,407		$	6,180
		Gains (Losses)
		Three Months ended September 30, 2013									Nine Months ended September 30, 2013
		Retail			Institutional			Total			Retail			Institutional			Total
	Futures contracts	$	(4,192	)	$	4,547		$	355		$	(13,958	)	$	15,710		$	1,752
	Total	$	(4,192	)	$	4,547		$	355		$	(13,958	)	$	15,710		$	1,752

Segments_Tables

Segments (Tables)	9 Months Ended
	Sep. 30, 2014
Segment Reporting [Abstract]	'
Schedule of Segment Reporting Information, by Segment	'
	Information concerning the Company’s operations by reportable segment is as follows, with amounts in thousands:
		Three Months Ended September 30, 2014
		Retail Trading			Institutional Trading			Corporate			Total
	Total revenues	$	91,861		$	23,926		$	360		$	116,147
	Total expenses	52,284			27,859			31,724			111,867
	Loss on equity method investments	—			239			137			376
	Income (loss) before income taxes	$	39,577		$	(4,172	)	$	(31,501	)	$	3,904
		Three Months Ended September 30, 2013
		Retail Trading			Institutional Trading			Corporate			Total
	Total revenues	$	90,392		$	22,856		$	—		$	113,248
	Total expenses	56,900			20,721			41,785			119,406
	Loss (gain) on equity method investments	—			244			(61		)	183
	Income (loss) before income taxes	$	33,492		$	1,891		$	(41,724	)	$	(6,341	)
		Nine Months Ended September 30, 2014
		Retail Trading			Institutional Trading			Corporate			Total
	Total revenues	$	252,866		$	75,856		$	360		$	329,082
	Total expenses	156,122			81,049			91,903			329,074
	Loss on equity method investments	—			606			304			910
	Income (loss) before income taxes	$	96,744		$	(5,799	)	$	(91,847	)	$	(902	)
		Nine Months Ended September 30, 2013
		Retail Trading			Institutional Trading			Corporate			Total
	Total revenues	$	294,041		$	82,204		$	—		$	376,245
	Total expenses	166,332			73,636			89,317			329,285
	Loss on equity method investments	—			689			39			728
	Income (loss) before income taxes	$	127,709		$	7,879		$	(89,356	)	$	46,232
	Assets		As of September 30, 2014			As of December 31, 2013
	Retail		$	1,738,368		$	1,622,829
	Institutional		454,887			417,492
	Corporate		191,154			183,626
	Total assets		$	2,384,409		$	2,223,947

Description_of_Business_and_Ba3

Description of Business and Basis of Presentation - Additional Information (Detail)	Sep. 30, 2014	Dec. 31, 2013
Lucid LLP	'	'
Basis of Presentation [Line Items]	'	'
Noncontrolling equity interest	49.90%	'
FXCM Holdings, LLC	'	'
Basis of Presentation [Line Items]	'	'
Parent ownership interest	56.40%	54.80%
Noncontrolling equity interest	43.60%	45.20%

Holdings_Change_in_Interest_Ho

Holdings - Change in Interest Holdings of Corporation and Non-Controlling Interest (Detail)	9 Months Ended
	Sep. 30, 2014
Stockholders' Equity Attributable to Noncontrolling Interest [Roll Forward]	'
Exercise of stock options (in shares)	266,500
Equity based compensation (in shares)	648,490
Controlling Units	'
Stockholders' Equity Attributable to Noncontrolling Interest [Roll Forward]	'
Balance at January 1, 2014 (in shares)	44,664,884
Balance as of January 1, 2014 (percent)	54.80%
Holding units acquired by FXCM Inc. related to exchanges of Holdings units for shares of Class A common stock (in shares)	1,155,359
Holdings units acquired by FXCM Inc. related to exchanges of Holdings units for shares of Class A common stock (percent)	1.40%
Holding units repurchased related to Class A common stock repurchased (in shares)	-45,985
Holding units repurchased related to Class A common stock repurchased (percent)	0.00%
Exercise of stock options (in shares)	266,500
Exercise of stock options (percent)	0.10%
Equity based compensation (in shares)	163,832
Issuance under equity based compensation (percent)	0.10%
Balance at September 30, 2014 (in shares)	46,204,590
Balance as of September 30, 2014 (percent)	56.40%
Non-Controlling Units	'
Stockholders' Equity Attributable to Noncontrolling Interest [Roll Forward]	'
Balance at January 1, 2014 (in shares)	36,835,821
Balance as of January 1, 2014 (percent)	45.20%
Holding units acquired by FXCM Inc. related to exchanges of Holdings units for shares of Class A common stock (in shares)	-1,155,359
Holdings units acquired by FXCM Inc. related to exchanges of Holdings units for shares of Class A common stock (percent)	-1.40%
Holding units repurchased related to Class A common stock repurchased (in shares)	0
Holding units repurchased related to Class A common stock repurchased (percent)	0.00%
Exercise of stock options (in shares)	0
Exercise of stock options (percent)	-0.10%
Equity based compensation (in shares)	0
Issuance under equity based compensation (percent)	-0.10%
Balance at September 30, 2014 (in shares)	35,680,462
Balance as of September 30, 2014 (percent)	43.60%
Total Units	'
Stockholders' Equity Attributable to Noncontrolling Interest [Roll Forward]	'
Balance at January 1, 2014 (in shares)	81,500,705
Balance as of January 1, 2014 (percent)	100.00%
Holding units acquired by FXCM Inc. related to exchanges of Holdings units for shares of Class A common stock (in shares)	0
Holdings units acquired by FXCM Inc. related to exchanges of Holdings units for shares of Class A common stock (percent)	0.00%
Holding units repurchased related to Class A common stock repurchased (in shares)	-45,985
Holding units repurchased related to Class A common stock repurchased (percent)	0.00%
Exercise of stock options (in shares)	266,500
Exercise of stock options (percent)	0.00%
Equity based compensation (in shares)	163,832
Issuance under equity based compensation (percent)	0.00%
Balance at September 30, 2014 (in shares)	81,885,052
Balance as of September 30, 2014 (percent)	100.00%

Business_Acquisition_Additiona

Business Acquisition - Additional Information (Detail) (USD $)

9 Months Ended

0 Months Ended

3 Months Ended

9 Months Ended

0 Months Ended

1 Months Ended

9 Months Ended

Sep. 30, 2014

Sep. 30, 2013

Dec. 31, 2013

Jan. 21, 2014

Sep. 30, 2014

Sep. 30, 2014

Sep. 30, 2014

Jan. 21, 2014

Sep. 20, 2013

Mar. 31, 2014

Dec. 31, 2013

Sep. 30, 2014

Sep. 20, 2013

V3

V3

V3

V3

V3

Faros

Faros

Faros

Faros

Faros

seller

Business Acquisition [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

'

Total fair value at acquisition date

'

'

'

'

$31,587,000

[1]

$31,587,000

[1]

$31,587,000

[1]

$32,500,000

'

'

'

'

$31,200,000

Liabilities incurred

'

'

'

12,100,000

'

'

'

'

'

'

'

'

'

Voting interest acquired

'

'

'

'

50.10%

50.10%

50.10%

'

'

'

'

'

50.10%

Goodwill

326,100,000

'

307,936,000

'

19,357,000

[1]

19,357,000

[1]

19,357,000

[1]

20,200,000

'

'

'

'

23,033,000

Non-Controlling interest

'

'

'

'

15,762,000

[1]

15,762,000

[1]

15,762,000

[1]

16,200,000

'

'

'

'

15,569,000

Decrease in purchase price

'

'

'

'

900,000

'

'

'

'

'

'

'

'

Decrease in goodwill recorded

'

'

'

'

800,000

'

'

'

'

'

'

'

'

Purchase price

'

'

'

'

'

'

'

'

5,000,000

'

'

'

'

Contingent consideration liability

'

'

'

'

'

'

'

'

'

3,700,000

'

'

10,600,000

Purchase price

'

'

'

16,300,000

'

15,825,000

[1]

'

'

15,631,000

'

'

'

'

Number of sellers follow-on payment payable to

'

'

'

'

'

'

'

'

'

'

'

'

1

Business acquisition equity interest issued remaining shares fair value

'

'

'

'

'

'

'

'

'

'

'

'

400,000

Discount rate

'

'

'

'

'

'

'

'

25.00%

'

'

'

'

Gain on Follow-on Payment

3,672,000

0

'

'

'

'

'

'

'

3,700,000

-6,900,000

'

'

Long-term annual earnings growth rate

'

'

'

'

'

'

'

'

3.00%

'

'

'

'

Remeasurement period

'

'

'

'

'

'

'

'

'

'

'

'12 months

'

Transaction costs

'

'

'

'

$0

'

$1,200,000

'

'

'

'

'

'

[1]

The amounts included in the V3 Purchase Price Allocation table represent the allocation of the purchase price and includes revisions made during the 12 months remeasurement period from the V3 Acquisition Date.

Business_Acquisition_Purchase_

Business Acquisition - Purchase Price Allocation (Detail) (USD $)

Sep. 30, 2014

Dec. 31, 2013

Jan. 21, 2014

Sep. 30, 2014

Jan. 21, 2014

Sep. 30, 2014

Sep. 30, 2014

Sep. 30, 2014

Sep. 20, 2013

Sep. 20, 2013

Sep. 20, 2013

Sep. 20, 2013

In Thousands, unless otherwise specified

V3

V3

V3

V3

V3

V3

Faros

Faros

Faros

Faros

Trading platform

Processing platform

Executory contract

Customer relationships

Trade Names

Business Acquisition [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

Purchase price

'

'

$16,300

$15,825

[1]

'

'

'

'

$15,631

'

'

'

Non-Controlling interest

'

'

'

15,762

[1]

16,200

'

'

'

'

15,569

'

'

Total fair value at Acquisition Date

'

'

'

31,587

[1]

32,500

'

'

'

'

31,200

'

'

Net assets acquired

'

'

'

10,210

[1]

'

'

'

'

'

137

'

'

Adjustments to reflect acquired assets and liabilities at fair value

'

'

'

'

'

'

'

'

'

'

'

'

Intangible assets other than goodwill

'

'

'

'

'

950

[1],[2]

150

[1],[3]

470

[1],[4]

'

'

6,000

[5]

130

[6]

Non-compete agreements

'

'

'

450

[1],[7]

'

'

'

'

'

1,900

[8]

'

'

Fair value of net assets acquired

'

'

'

12,230

[1]

12,230

'

'

'

'

8,167

'

'

Goodwill resulting from acquisitions

$326,100

$307,936

'

$19,357

[1]

$20,200

'

'

'

'

$23,033

'

'

[1]

The amounts included in the V3 Purchase Price Allocation table represent the allocation of the purchase price and includes revisions made during the 12 months remeasurement period from the V3 Acquisition Date.

[2]

Consists of internally developed software platforms that support trade execution, with an amortization life of 4 years.

[3]

Consists of an internally developed software platform that supports trading, with an amortization life of 5 years.

[4]

Consists of a service agreements relating to fiber optics, wireless and other services, with an amortization life of 3 years.

[5]

Consists of institutional and bank customers, with an amortization life of 4 years.

[6]

Amortization life is 3 years.

[7]

Amortization life is 1 year.

[8]

Amortization life is 9 years.

Business_Acquisition_Purchase_1

Business Acquisition - Purchase Price Allocation (Parenthetical) (Detail)	0 Months Ended
	Jan. 21, 2014	Jan. 21, 2014	Jan. 21, 2014	Jan. 21, 2014	Sep. 20, 2013	Sep. 20, 2013	Sep. 20, 2013
	V3	V3	V3	V3	Faros	Faros	Faros
	Trading platform	Processing platform	Noncompete Agreements	Executory contract	Noncompete Agreements	Customer relationships	Trade Names
Business Acquisition [Line Items]	'	'	'	'	'	'	'
Useful life	'4 years	'5 years	'1 year	'3 years	'9 years	'4 years	'3 years

Business_Acquisition_Condensed

Business Acquisition - Condensed Statement of Net Assets Acquired (Details) (USD $)	Sep. 30, 2014		Jan. 21, 2014	Sep. 20, 2013
In Thousands, unless otherwise specified	V3		V3	Faros
Assets	'		'	'
Cash and cash equivalents	'		'	$1,055
Accounts receivable, net	'		'	40
Office, communication and computer equipment, net	'		973	31
Intangible assets	'		2,020	8,030
Exchange memberships and common equity shares	'		6,429	'
Equity method investments, net	'		1,523	'
Other assets	'		1,392	76
Total assets	'		12,337	9,232
Liabilities	'		'	'
Accounts payable and accrued expenses	'		'	1,065
Total liabilities	'		107	1,065
Fair value of net assets acquired	$12,230	[1]	$12,230	$8,167
[1]	The amounts included in the V3 Purchase Price Allocation table represent the allocation of the purchase price and includes revisions made during the 12 months remeasurement period from the V3 Acquisition Date.

Business_Acquisition_Pro_Forma

Business Acquisition - Pro Forma Condensed Combined Financial Information of Acquisitions (Detail) (USD $)	3 Months Ended		9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014
					V3
Business Acquisition [Line Items]	'	'	'	'	'
Total revenues	$116,147	$124,181	$329,082	$416,843	$14,384
Net Income (loss)	$2,760	($9,249)	($4,615)	$33,856	($2,052)

Restricted_Time_Deposits_Addit

Restricted Time Deposits - Additional Information (Detail) (USD $)	Sep. 30, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Cash and Cash Equivalents [Abstract]	'	'
Current restricted time deposits	$3,648	$0
Current restricted time deposits, rate	0.03%	'
Noncurrent restricted time deposits	$5,472	'
Noncurrent restricted time deposits, rate	0.03%	'

Trading_Securities_Additional_

Trading Securities - Additional Information (Details) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2013
Investments, Debt and Equity Securities [Abstract]	'	'	'	'	'
Trading securities	$633,000	'	$633,000	'	$0
Net realized and unrealized gain (loss) on trading securities	$2,300,000	$0	$3,300,000	$0	'

Accounts_Receivable_and_Other_2

Accounts Receivable and Other Receivables - Additional Information (Details) (USD $)	Sep. 30, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Accounts and Other Receivables, Net, Current [Abstract]	'	'
Total accounts and other receivables	$20,344	$19,806
Accounts receivable, net	'	'
Accounts and Other Receivables, Net, Current [Abstract]	'	'
Total accounts and other receivables	11,323	9,953
Notes receivable	'	'
Accounts and Other Receivables, Net, Current [Abstract]	'	'
Total accounts and other receivables	0	5,992
Tax receivable	'	'
Accounts and Other Receivables, Net, Current [Abstract]	'	'
Total accounts and other receivables	$9,021	$3,861

Equity_Method_Investment_Addit

Equity Method Investment - Additional Information (Detail) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2014	Sep. 30, 2014	Jan. 21, 2014	Jan. 21, 2014
					Other Assets	Other Assets	Electric Communication Network for Foreign Exchange Trading	FX Trading Software Developer	Entity that Holds Interest in a Firm that Provides a Financial Intelligence Platform	Firm that Provides a Financial Intelligence Platform
Schedule of Equity Method Investments [Line Items]	'	'	'	'	'	'	'	'	'	'
Percentage of equity interest	'	'	'	'	'	'	35.30%	21.80%	66.30%	17.26%
Carrying value of equity method investments	'	'	'	'	$10,400,000	$9,800,000	'	'	'	'
Loss on equity investment	$376,000	$183,000	$910,000	$728,000	'	'	'	'	'	'

Earnings_Per_Share_Additional_

Earnings Per Share - Additional Information (Detail) (USD $)

9 Months Ended

9 Months Ended

3 Months Ended

9 Months Ended

1 Months Ended

0 Months Ended

3 Months Ended

9 Months Ended

Sep. 30, 2014

Sep. 30, 2013

Dec. 21, 2012

Jun. 30, 2013

Sep. 30, 2014

Sep. 30, 2014

Sep. 30, 2014

Jun. 30, 2013

Jun. 08, 2012

Sep. 30, 2013

Sep. 30, 2014

Sep. 30, 2014

Sep. 30, 2014

Sep. 30, 2014

Senior Notes

Common Class A

Common Class A

Common Class A

Common Class A

Common Class A

Common Class A

Common Class A

Common Class A

Common Class A

Common Class A

2.25% Senior Convertible Notes

Controlling Units

Controlling Units

Senior Notes

Common Stock

Common Stock

Common Stock

Independent Directors Option

Employee Stock Option

Third Anniversary, Shares Issued

2.25% Senior Convertible Notes

Lucid LLP

Lucid LLP

Lucid LLP

Lucid LLP

Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Stock options granted to purchase shares

648,490

'

'

'

'

'

'

'

'

'

'

83,490

565,000

'

Stock option granted excluded from computation of earnings per share

1,039,490

7,611,390

'

'

'

'

'

'

'

'

'

'

'

'

Business acquisitions, shares issued

'

'

'

'

'

'

'

'

7,200,000

1,200,000

3,000,000

'

'

'

Business acquisition, shares issued if profit target is achieved

'

'

'

'

'

'

'

'

'

'

'

'

'

3,000,000

Face amount

'

'

'

$172,500,000

'

'

'

'

'

'

'

'

'

'

Interest rate

'

'

2.25%

2.25%

'

'

'

'

'

'

'

'

'

'

Conversion ratio

'

'

'

'

'

'

'

0.0532992

'

'

'

'

'

'

Conversion price

'

'

'

$18.76

'

'

'

'

'

'

'

'

'

'

Conversion ratio

'

'

'

'

1

'

'

'

'

'

'

'

'

'

Holding units acquired by FXCM Inc. related to exchanges of Holdings units for shares of Class A common stock (in shares)

'

'

'

'

'

100,000

1,200,000

'

'

'

'

'

'

'

Earnings_Per_Share_Reconciliat

Earnings Per Share - Reconciliation of Numerator and Denominator Used in Basic and Diluted EPS Calculations (Detail) (USD $)	3 Months Ended		9 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Numerator	'	'	'	'
Net income (loss) available to holders of Class A common stock	$2,392	($5,122)	$1,391	$11,862
Add dilutive effect of the following:	'	'	'	'
Dilutive weighted average shares of Class A common stock	43,819	34,469	42,367	32,009
Basic income per share of Class A common stock (in dollars per share)	$0.06	($0.15)	$0.03	$0.38
Diluted income per share of Class A common stock (in dollars per share)	$0.05	($0.15)	$0.03	$0.37
Common Class A	'	'	'	'
Numerator	'	'	'	'
Net income (loss) available to holders of Class A common stock	2,392	-5,122	1,391	11,862
Earnings allocated to participating securities	0	0	0	0
Earnings available for common stockholders	$2,392	($5,122)	$1,391	$11,862
Denominator for basic net income per share of Class A common stock	'	'	'	'
Weighted average shares of Class A common stock	42,963	33,718	40,108	30,983
Add dilutive effect of the following:	'	'	'	'
Stock options	856	751	878	288
Convertible note hedges	0	0	0	0
Warrants	0	0	0	0
Dilutive weighted average shares of Class A common stock	43,819	34,469	42,367	32,009
Basic income per share of Class A common stock (in dollars per share)	$0.06	($0.15)	$0.03	$0.38
Diluted income per share of Class A common stock (in dollars per share)	$0.05	($0.15)	$0.03	$0.37
First Anniversary, Shares Issued | Lucid LLP | Common Class A	'	'	'	'
Add dilutive effect of the following:	'	'	'	'
Weighted average of Lucid's anniversary shares	0	0	0	738
Second Anniversary, Shares Issued | Lucid LLP | Common Class A	'	'	'	'
Add dilutive effect of the following:	'	'	'	'
Weighted average of Lucid's anniversary shares	0	0	1,381	0

Related_Party_Transactions_Amo

Related Party Transactions - Amounts Receivable From, And Payable To, Related Parties (Detail) (USD $)	Sep. 30, 2014	Dec. 31, 2013
Receivables	'	'
Advances to Holdings non-controlling members	$305,000	$940,000
Due from related parties	10,196,000	1,766,000
Advances to employees	720,000	826,000
Payables	'	'
Employees	1,797,000	708,000
Shareholders with greater than 5% ownership in the Company	0	200,000
Tax receivable agreement	151,838,000	150,257,000
Follow-on Payment	0	3,672,000
Due to related parties	174,815,000	182,995,000
Lucid LLP	'	'
Receivables	'	'
Due from related parties	968,000	0
Notes receivable and interest - Lucid non-controlling members	8,203,000	0
Holding Non Controlling Units	'	'
Payables	'	'
Due to Other Related Parties	7,159,000	9,826,000
Lucid non controlling units - trade settlements	'	'
Payables	'	'
Due to Other Related Parties	0	169,000
Lucid non controlling units - acquisition	'	'
Payables	'	'
Due to Other Related Parties	7,460,000	9,800,000
Cash and Cash Equivalents Held for Customers	'	'
Payables	'	'
Guarantee agreement	'	8,400,000
Cash and Cash Equivalents Held for Customers | Monetary Credit Group LLC	'	'
Payables	'	'
Guarantee agreement	$6,561,000	$8,363,000

Related_Partly_Transactions_Ad

Related Partly Transactions - Additional Information (Detail) (USD $)

3 Months Ended

9 Months Ended

9 Months Ended

3 Months Ended

9 Months Ended

3 Months Ended

9 Months Ended

3 Months Ended

9 Months Ended

0 Months Ended

9 Months Ended

Share data in Thousands, unless otherwise specified

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2014

Sep. 30, 2013

Dec. 31, 2013

Dec. 21, 2012

Sep. 30, 2014

Sep. 30, 2013

Dec. 31, 2013

Sep. 30, 2014

Dec. 31, 2013

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2014

Dec. 31, 2013

Sep. 30, 2014

Sep. 30, 2014

Sep. 30, 2014

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2013

Dec. 31, 2013

Nov. 30, 2013

Sep. 30, 2014

Sep. 30, 2014

Sep. 30, 2014

Dec. 31, 2013

Sep. 30, 2014

Dec. 31, 2013

Sep. 30, 2014

Dec. 31, 2013

Sep. 30, 2014

Dec. 31, 2013

Sep. 30, 2014

Dec. 31, 2013

Jan. 21, 2014

Sep. 30, 2014

Jan. 21, 2014

Common Class A

Common Class A

Cash and Cash Equivalents Held for Customers

Other Liabilities

Other Liabilities

Global Finance and Master Capital

Global Finance and Master Capital

Global Finance and Master Capital

Global Finance and Master Capital

Lucid LLP

Lucid LLP

Lucid LLP

Shareholders With a Greater Than 5% Ownership

Shareholders With a Greater Than 5% Ownership

Shareholder great than a 5% ownership

Method Credit Fund

Method Credit Fund

Method Credit Fund

Method Credit Fund

Method Credit Fund

Monetary Credit Group LLC

Monetary Credit Group LLC

Monetary Credit Group LLC

Monetary Credit Group LLC

Monetary Credit Group LLC

Lucid non controlling units - trade settlements

Lucid non controlling units - trade settlements

Holding Non Controlling Units

Holding Non Controlling Units

Lucid non controlling units - acquisition

Lucid non controlling units - acquisition

V3

V3

V3

Accounts receivable, net

Maximum

Global Finance and Master Capital

Cash and Cash Equivalents Held for Customers

Cash and Cash Equivalents Held for Customers

Cash and Cash Equivalents Held for Customers

Related Party Transaction [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Purchase price

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

$16,300,000

$15,825,000

[1]

'

Non-Controlling interest

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

15,762,000

[1]

16,200,000

Notes receivable and interest - Lucid non-controlling members

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

8,100,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Interest rate

'

'

'

'

'

2.25%

'

'

'

'

'

'

'

'

'

2.00%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Due from related parties

10,196,000

'

10,196,000

'

1,766,000

'

'

'

'

'

'

'

'

'

'

968,000

0

200,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Advances to the Lucid non-controlling members

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

800,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Percentage of employee and shareholders ownership

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

5.00%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Percentage of ownership interests

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

90.00%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Referring broker fees

20,998,000

20,709,000

56,615,000

64,481,000

'

'

'

'

'

'

'

300,000

400,000

900,000

1,200,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Percentage of equity interest

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

5.00%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Guarantee agreement

'

'

'

'

'

'

'

'

8,400,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

0

0

'

'

'

6,561,000

8,363,000

'

'

'

'

'

'

'

'

'

Proceeds from Related Parties

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

0

0

'

'

'

0

0

'

'

'

'

'

'

'

'

'

'

'

'

Aggregate amount of margin extended under the monetary guaranty

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

0

'

'

12,900,000

12,900,000

4,500,000

'

'

'

'

'

'

'

'

'

'

'

Guarantor Obligation, Fees Collected

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

300,000

500,000

'

'

'

'

'

'

'

'

'

'

'

'

Due to Other Related Parties

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

0

169,000

7,159,000

9,826,000

7,460,000

9,800,000

'

'

'

Contingent consideration liability

'

'

'

'

'

'

'

'

'

0

3,700,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Conversion ratio

'

'

'

'

'

'

1

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Exchange of Holding Units into Class A common stock

'

'

'

'

'

'

1,155

8,600

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Tax receivable agreement

151,838,000

'

151,838,000

'

150,257,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Pursuant to tax receivable agreement

'

'

$3,707,000

$4,079,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

[1]

The amounts included in the V3 Purchase Price Allocation table represent the allocation of the purchase price and includes revisions made during the 12 months remeasurement period from the V3 Acquisition Date.

StockBased_Compensation_Additi

Stock-Based Compensation - Additional Information (Detail) (USD $)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'	'	'	'
Contractual term	'	'	'7 years	'	'
Vesting period	'	'	'4 years	'	'
Granted (in shares)	'	'	648,490	'	'
Weighted average grant date fair value of stock options granted during the period	'	'	$5.66	$5.52	'
Unrecognized expense	$7,500,000	'	$7,500,000	'	'
Fair value of vested stock options	'	'	2,200,000	1,800,000	'
Capitalized compensation cost	'	'	900,000	'	1,400,000
Proceeds from Stock Options Exercised	2,100,000	19,200,000	3,608,000	21,877,000	'
Period of common stock publicly traded	'	'	'4 years	'	'
Non Employee Director Stock Option | Common Class A	'	'	'	'	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'	'	'	'
Granted (in shares)	'	'	83,490	'	'
Employee Stock Option	'	'	'	'	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'	'	'	'
Weighted average grant date fair value of stock options granted during the period	$0	$6.98	$5.70	$5.99	'
Recognition period	'	'	'2 years 2 months 12 days	'	'
Employee Stock Option | Common Class A	'	'	'	'	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'	'	'	'
Granted (in shares)	'	'	565,000	'	'
Independent Directors Options	'	'	'	'	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'	'	'	'
Weighted average grant date fair value of stock options granted during the period	$0	$0	$5.39	$4.26	'
Compensation and Benefits | Employee Stock Option	'	'	'	'	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'	'	'	'
Compensation expense	2,600,000	2,500,000	7,500,000	7,200,000	'
Compensation and Benefits | Independent Directors Options	'	'	'	'	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'	'	'	'
Compensation expense	$100,000	'	$300,000	$300,000	'

StockBased_Compensation_Summar

Stock-Based Compensation - Summary of Company's Stock Options Activity Under LTIP (Detail) (USD $)	9 Months Ended	12 Months Ended
	Sep. 30, 2014	Dec. 31, 2013
Shares	'	'
Outstanding at January 1, 2014 (in shares)	7,607,800	'
Granted (in shares)	648,490	'
Exercised (in shares)	-266,500	'
Forfeited or expired (in shares)	-209,900	'
Outstanding as of March 31, 2014 (in shares)	7,779,890	7,607,800
Vested or expected to vest at end of period (in shares)	7,704,862	'
Exercisable as of end period (in shares)	4,632,150	'
Weighted- Average Exercise Price	'	'
Outstanding at January 1, 2014 (in dollars per share)	$13.48	'
Granted (in dollars per share)	$16.28	'
Exercised (in dollars per share)	$13.54	'
Forfeited or expired (in dollars per share)	$13.10	'
Outstanding as March 31, 2014 (in dollars per share)	$13.72	$13.48
Vested or expected to vest at end of period (in dollars per share)	$13.73	'
Exercisable as of end period (in dollars per share)	$13.52	'
Weighted- Average Remaining Contractual Term	'	'
Outstanding as beginning period	'3 years 9 months 22 days	'4 years 3 months 18 days
Vested or expected to vest at end period	'3 years 9 months 22 days	'
Exercisable as end period	'3 years 5 months 5 days	'

StockBased_Compensation_Assump

Stock-Based Compensation - Assumptions used in Black Scholes Valuation Model (Detail) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Assumptions used to Determine Fair Value Options [Line Items]	'	'	'	'
Estimated fair value at grant date (in dollars per share)	'	'	$5.66	$5.52
Independent Directors Options	'	'	'	'
Assumptions used to Determine Fair Value Options [Line Items]	'	'	'	'
Expected term in years	'0 years	'0 years	'4 years	'4 years
Risk-free interest rate	0.00%	0.00%	1.19%	0.63%
Expected volatility	0.00%	0.00%	44.00%	54.00%
Dividend yield	0.00%	0.00%	1.43%	2.05%
Estimated fair value at grant date (in dollars per share)	$0	$0	$5.39	$4.26
Employee Stock Option	'	'	'	'
Assumptions used to Determine Fair Value Options [Line Items]	'	'	'	'
Expected term in years	'0 years	'4 years 9 months	'4 years 9 months	'4 years 9 months
Risk-free interest rate	0.00%	1.28%	1.58%	0.99%
Expected volatility	0.00%	50.00%	45.00%	50.00%
Dividend yield	0.00%	1.33%	1.48%	1.60%
Estimated fair value at grant date (in dollars per share)	$0	$6.98	$5.70	$5.99

Stockholders_Equity_Changes_in

Stockholders' Equity - Changes in Company's Class A Common Stock Shares Outstanding (Detail)	9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013
Stockholders' Equity Note [Roll Forward]	'	'
Stock options exercised	266,500	'
Class A common stock	'	'
Stockholders' Equity Note [Roll Forward]	'	'
Balance at January 1, 2014 (in shares)	44,664,884	'
Issued	164,000	'
Exchange of Holding Units into Class A common stock	1,155,000	8,600,000
Repurchased	-46,000	'
Stock options exercised	267,000	'
Balance at September 30, 2014 (in shares)	46,204,590	'

Stockholders_Equity_Additional

Stockholders' Equity - Additional Information (Detail) (Class B common stock)	Sep. 30, 2014	Dec. 31, 2013
Class B common stock	'	'
Class of Stock [Line Items]	'	'
Class B common stock issued	34	41

Minimum_Net_Capital_Requiremen2

Minimum Net Capital Requirements - Minimum Capital Requirement And Excess Capital (Detail) (USD $)	Sep. 30, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
US	'	'
Capital Requirements on Foreign Financial Institutions [Line Items]	'	'
Capital	$52.20	$64.20
Minimum capital requirement	30.4	27.1
Excess capital	21.8	37.1
HK	'	'
Capital Requirements on Foreign Financial Institutions [Line Items]	'	'
Capital	31.9	33.6
Minimum capital requirement	13.5	12.3
Excess capital	18.4	21.3
UK LTD	'	'
Capital Requirements on Foreign Financial Institutions [Line Items]	'	'
Capital	109.3	86
Minimum capital requirement	33	24.7
Excess capital	76.3	61.3
Australia	'	'
Capital Requirements on Foreign Financial Institutions [Line Items]	'	'
Capital	1.4	4.7
Minimum capital requirement	0.9	0.4
Excess capital	0.5	4.3
ODL	'	'
Capital Requirements on Foreign Financial Institutions [Line Items]	'	'
Capital	26.2	18.4
Minimum capital requirement	4.3	6.9
Excess capital	21.9	11.5
FSL	'	'
Capital Requirements on Foreign Financial Institutions [Line Items]	'	'
Capital	41.7	34.8
Minimum capital requirement	6.6	8.2
Excess capital	35.1	26.6
FXCMJ	'	'
Capital Requirements on Foreign Financial Institutions [Line Items]	'	'
Capital	35.7	36.3
Minimum capital requirement	5.2	5.6
Excess capital	30.5	30.7
Lucid LLP	'	'
Capital Requirements on Foreign Financial Institutions [Line Items]	'	'
Capital	16.6	41.8
Minimum capital requirement	2.7	4.2
Excess capital	13.9	37.6
Faros	'	'
Capital Requirements on Foreign Financial Institutions [Line Items]	'	'
Capital	0	0.1
Minimum capital requirement	0	0
Excess capital	$0	$0.10

Litigation_Additional_Informat

Litigation - Additional Information (Detail)	3 Months Ended	9 Months Ended	1 Months Ended		3 Months Ended		1 Months Ended
	Sep. 30, 2014	Sep. 30, 2014	Feb. 28, 2014	Feb. 28, 2014	Mar. 31, 2013	Dec. 31, 2012	Jan. 31, 2014	Feb. 28, 2014	Jul. 31, 2014	Sep. 30, 2014
	USD ($)	USD ($)	FCA Draft Warning Notice	FCA Draft Warning Notice	JFSA	JFSA	US vs Revelation Forex Fund, Kevin G. White, and Related Entities	Restitution to Affected Clients	US vs. National Futures Association	US vs. National Futures Association
			USD ($)	GBP (£)	USD ($)	USD ($)	USD ($)	FCA Draft Warning Notice	USD ($)	USD ($)
								Maximum
								USD ($)
Loss Contingencies [Line Items]	'	'	'	'	'	'	'	'	'	'
Accrual	$15,000,000	$15,000,000	'	'	'	$2,600,000	'	'	'	$1,000,000
Settlement amount	'	'	6,600,000	4,000,000	2,300,000	'	'	9,900,000	200,000	'
Damages sought	'	'	'	'	'	'	3,800,000	'	'	'
Litigation expense	700,000	2,500,000	'	'	'	'	'	'	'	'
Range of loss, min	0	0	'	'	'	'	'	'	'	'
Range of loss, max	$4,700,000	$4,700,000	'	'	'	'	'	'	'	'

Debt_Additional_Information_De

Debt - Additional Information (Details) (USD $)

0 Months Ended

3 Months Ended

9 Months Ended

9 Months Ended

3 Months Ended

3 Months Ended

9 Months Ended

1 Months Ended

3 Months Ended

9 Months Ended

1 Months Ended

0 Months Ended

3 Months Ended

9 Months Ended

Dec. 21, 2012

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2014

Sep. 30, 2013

Dec. 21, 2012

Sep. 30, 2014

Jun. 06, 2014

Sep. 30, 2013

Dec. 21, 2012

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2014

Sep. 30, 2013

Jun. 30, 2013

Sep. 30, 2014

Dec. 31, 2013

Sep. 30, 2013

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2014

Sep. 30, 2013

Jun. 30, 2013

Jun. 30, 2013

Dec. 21, 2012

Sep. 30, 2014

Dec. 21, 2012

Sep. 30, 2014

Dec. 21, 2012

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2014

Sep. 30, 2013

Dec. 31, 2013

Dec. 21, 2012

Dec. 19, 2011

Sep. 30, 2014

Sep. 30, 2014

Sep. 30, 2014

Sep. 30, 2014

Lucid LLP

Lucid LLP

Lucid LLP

Unsecured Promissory Note One

Convertible Debt

Convertible Debt

Convertible Debt

Convertible Debt

Convertible Debt

Convertible Debt

Convertible Debt

Convertible Debt

Convertible Debt

Convertible Debt

Convertible Debt

Convertible Debt

Senior Notes

Senior Notes

Unsecured Promissory Note

Unsecured Promissory Note

Unsecured Promissory Note

Unsecured Promissory Note

Unsecured Promissory Note

Revolving Credit Facility

Revolving Credit Facility

Revolving Credit Facility

Revolving Credit Facility

Revolving Credit Facility

Revolving Credit Facility

Revolving Credit Facility

Revolving Credit Facility

Revolving Credit Facility

Minimum

Maximum

Restatement Adjustment

2.25% Senior Convertible Notes

2.25% Senior Convertible Notes

2.25% Senior Convertible Notes

2.25% Senior Convertible Notes

2.25% Senior Convertible Notes

2.25% Senior Convertible Notes

2.25% Senior Convertible Notes

2.25% Senior Convertible Notes

2.25% Senior Convertible Notes

2.25% Senior Convertible Notes

Lucid LLP

Lucid LLP

Federal Funds Rate

Eurodollar

Revolving Credit Facility

Revolving Credit Facility

D

Interest on Borrowings

Interest on Borrowings

Interest on Borrowings

Interest on Borrowings

Common Class A

D

Debt Instrument [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Percentage of equity interest of foreign subsidiaries pledged as collateral

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

65.00%

'

'

'

'

Current borrowing capacity

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

$22,900,000

'

'

$150,000,000

'

$150,000,000

'

'

'

'

'

'

'

'

Amount outstanding

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

30,000,000

'

30,000,000

'

0

'

'

'

'

'

'

Derivative, Basis Spread on Variable Rate

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

0.50%

1.00%

'

'

Interest on borrowings

'

3,028,000

2,869,000

9,121,000

4,976,000

'

'

'

'

'

970,000

970,000

2,911,000

1,272,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

400,000

100,000

1,200,000

1,300,000

'

'

'

'

'

'

'

Net capital required ratio

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

125.00%

'

Interest coverage ratio

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

4

'

Consolidated net leverage ratio

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

2.75

'

Consolidated Senior Leverage Ratio

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

1.5

'

Net unhedged exposure

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

20.00%

Net unhedged non foreign currency exposure

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

10.00%

Weighted Average Dollar Amount Of Borrowings Related To Credit Agreement

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

27,700,000

0

37,500,000

46,700,000

'

'

'

'

'

'

'

Debt, Weighted Average Interest Rate During Period

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

2.90%

0.00%

2.68%

2.44%

'

'

'

'

'

'

'

Face amount

'

'

'

'

'

'

'

'

'

71,400,000

'

'

'

'

172,500,000

'

'

172,500,000

'

'

'

'

172,500,000

'

'

'

'

'

'

'

'

'

'

'

15,800,000

'

'

'

'

'

Interest rate

'

'

'

'

'

2.25%

'

'

'

'

'

'

'

'

2.25%

'

'

'

'

'

'

'

2.25%

'

'

2.25%

2.25%

2.25%

3.50%

'

'

'

'

'

'

'

'

'

'

'

Proceeds from issuance of senior convertibles notes, net

'

'

'

'

'

'

'

'

'

'

'

'

'

'

166,500,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Conversion ratio

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

0.0532992

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Conversion price

'

'

'

'

'

'

'

'

'

'

'

'

'

'

$18.76

'

'

'

'

'

'

'

$18.76

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Threshold trading days

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

20

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Threshold consecutive trading days

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'30 days

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Threshold percentage of greater than or equal stock price

'

'

'

'

'

'

'

'

'

'

'

'

'

'

130.00%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Measurement period, business days

'

'

'

'

'

'

'

'

'

'

'

'

'

'

5

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Measurement period, trading days

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'5 days

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Threshold percentage of less than stock price

'

'

'

'

'

'

'

'

'

'

'

'

'

'

98.00%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Repurchase percentage under certain conditions

'

'

'

'

'

'

'

'

'

'

'

'

'

'

100.00%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Exercise price of warrants (in dollars per share)

'

'

$21.24

'

$21.24

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Cost of hedge

'

'

'

'

29,100,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Proceeds from sale of warrants

'

'

'

0

18,578,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Equity component

'

'

'

'

'

'

'

'

'

'

29,101,000

'

29,101,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Convertible notes

'

'

'

'

'

'

'

'

'

'

150,236,000

'

150,236,000

'

'

'

'

144,100,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Effective interest rate

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

6.20%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Unamortized debt issuance cost

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

4,400,000

5,300,000

6,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Amortization of Financing Costs

'

'

'

1,381,000

815,000

'

'

'

'

'

'

'

'

'

'

'

'

'

300,000

300,000

900,000

400,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Repayments of Notes Payable

64,000,000

'

'

2,300,000

'

'

5,500,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Purchase price

'

'

'

'

'

'

'

'

15,300,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Term

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'6 months

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Notes Payable

'

$7,500,000

'

$7,500,000

'

'

'

$9,800,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Debt_Applicable_Margin_and_Com

Debt - Applicable Margin and Commitment Fees (Details) (Revolving Credit Facility)	9 Months Ended
	Sep. 30, 2014
Less than 0.50 to 1.00	'
Debt Instrument [Line Items]	'
Commitment Fee	0.25%
Less than 0.50 to 1.00 | Eurodollar	'
Debt Instrument [Line Items]	'
Applicable Margin	1.75%
Less than 0.50 to 1.00 | Base Rate	'
Debt Instrument [Line Items]	'
Applicable Margin	0.75%
Greater than or equal to 0.50 to 1.00 but less than 1.00 to 1.00	'
Debt Instrument [Line Items]	'
Commitment Fee	0.30%
Greater than or equal to 0.50 to 1.00 but less than 1.00 to 1.00 | Eurodollar	'
Debt Instrument [Line Items]	'
Applicable Margin	2.00%
Greater than or equal to 0.50 to 1.00 but less than 1.00 to 1.00 | Base Rate	'
Debt Instrument [Line Items]	'
Applicable Margin	1.00%
Greater than or equal to 1.00 to 1.00 but less than 1.50 to 1.00	'
Debt Instrument [Line Items]	'
Commitment Fee	0.35%
Greater than or equal to 1.00 to 1.00 but less than 1.50 to 1.00 | Eurodollar	'
Debt Instrument [Line Items]	'
Applicable Margin	2.25%
Greater than or equal to 1.00 to 1.00 but less than 1.50 to 1.00 | Base Rate	'
Debt Instrument [Line Items]	'
Applicable Margin	1.25%
Greater than or equal to 1.50 to 1.00, but less than 2.00 to 1.00	'
Debt Instrument [Line Items]	'
Commitment Fee	0.40%
Greater than or equal to 1.50 to 1.00, but less than 2.00 to 1.00 | Eurodollar	'
Debt Instrument [Line Items]	'
Applicable Margin	2.50%
Greater than or equal to 1.50 to 1.00, but less than 2.00 to 1.00 | Base Rate	'
Debt Instrument [Line Items]	'
Applicable Margin	1.50%
Greater than or equal to 2.00 to 1.00	'
Debt Instrument [Line Items]	'
Commitment Fee	0.45%
Greater than or equal to 2.00 to 1.00 | Eurodollar	'
Debt Instrument [Line Items]	'
Applicable Margin	2.75%
Greater than or equal to 2.00 to 1.00 | Base Rate	'
Debt Instrument [Line Items]	'
Applicable Margin	1.75%
Minimum | Greater than or equal to 0.50 to 1.00 but less than 1.00 to 1.00	'
Debt Instrument [Line Items]	'
Consolidated Leverage Ratio	0.5
Minimum | Greater than or equal to 1.00 to 1.00 but less than 1.50 to 1.00	'
Debt Instrument [Line Items]	'
Consolidated Leverage Ratio	1
Minimum | Greater than or equal to 1.50 to 1.00, but less than 2.00 to 1.00	'
Debt Instrument [Line Items]	'
Consolidated Leverage Ratio	1.5
Minimum | Greater than or equal to 2.00 to 1.00	'
Debt Instrument [Line Items]	'
Consolidated Leverage Ratio	2
Maximum | Less than 0.50 to 1.00	'
Debt Instrument [Line Items]	'
Consolidated Leverage Ratio	0.5
Maximum | Greater than or equal to 0.50 to 1.00 but less than 1.00 to 1.00	'
Debt Instrument [Line Items]	'
Consolidated Leverage Ratio	1
Maximum | Greater than or equal to 1.00 to 1.00 but less than 1.50 to 1.00	'
Debt Instrument [Line Items]	'
Consolidated Leverage Ratio	1.5
Maximum | Greater than or equal to 1.50 to 1.00, but less than 2.00 to 1.00	'
Debt Instrument [Line Items]	'
Consolidated Leverage Ratio	2

Debt_Convertible_Debt_Details

Debt - Convertible Debt (Details) (USD $)	3 Months Ended		9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Debt Instrument [Line Items]	'	'	'	'
Interest expense - stated coupon rate	$3,028	$2,869	$9,121	$4,976
Interest expense - amortization of deferred bond discount	'	'	3,933	1,644
Convertible Debt	'	'	'	'
Debt Instrument [Line Items]	'	'	'	'
Liability component - principal	172,500	'	172,500	'
Deferred bond discount	-22,264	'	-22,264	'
Liability component - net carrying value	150,236	'	150,236	'
Equity component	29,101	'	29,101	'
Interest expense - stated coupon rate	970	970	2,911	1,272
Interest expense - amortization of deferred bond discount	1,335	1,254	3,932	1,644
Total interest expense - convertible note	$2,305	$2,224	$6,843	$2,916

Commitments_and_Contingencies_

Commitments and Contingencies - Additional Information (Detail) (Variable Interest Entity, Primary Beneficiary, USD $)	0 Months Ended			3 Months Ended	9 Months Ended
In Millions, unless otherwise specified	Sep. 09, 2014	Apr. 03, 2014	Apr. 02, 2014	Sep. 30, 2014	Sep. 30, 2014
				General and Administrative Expense	General and Administrative Expense
Variable Interest Entity [Line Items]	'	'	'	'	'
Put options exercised	63.00%	'	37.00%	'	'
Payment on put options	$2.30	$1.30	'	'	'
Loss charged to earnings on put options	'	'	'	$2.30	$3.60

Exchange_Memberships_Additiona

Exchange Memberships - Additional Information (Details) (USD $)	9 Months Ended	12 Months Ended
	Sep. 30, 2014	Dec. 31, 2013
Exchange Memberships [Line Items]	'	'
Impairment of exchange membership	$0	$0
Other Assets | Ownership Interests	'	'
Exchange Memberships [Line Items]	'	'
Memberships in exchanges owned	2,800,000	'
Other Assets | Shares Owned	'	'
Exchange Memberships [Line Items]	'	'
Memberships in exchanges owned	$3,700,000	'

Fair_Value_Measurements_Fair_V

Fair Value Measurements - Fair Value Measured on a Recurring Basis (Details) (USD $)	Sep. 30, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Financial Assets:	'	'
Trading securities	$633	$0
Total derivative assets	58,418	84
Netting agreements	-54,614	-84
Total due to brokers	3,804	0
Financial Liabilities:	'	'
Total derivative liabilities	56,281	2,404
Netting agreements and cash collateral netting	-56,099	-84
Due to brokers total	182	2,320
Exchange traded options	'	'
Financial Assets:	'	'
Total derivative assets	4,049	'
Financial Liabilities:	'	'
Total derivative liabilities	7,764	'
Over the counter (OTC) options	'	'
Financial Liabilities:	'	'
Total derivative liabilities	1,457	'
Quoted Prices in Active Markets for Identical Assets (Level I)	'	'
Financial Assets:	'	'
Total assets	0	0
Financial Liabilities:	'	'
Total liabilities	0	0
Significant Observable Inputs (Level II)	'	'
Financial Assets:	'	'
Total assets	35,989	5,450
Financial Liabilities:	'	'
Total liabilities	180,643	155,750
Significant Unobservable Inputs (Level III)	'	'
Financial Assets:	'	'
Total assets	26,807	25,446
Financial Liabilities:	'	'
Total liabilities	7,460	9,800
Fair Value, Measurements, Recurring	'	'
Financial Assets:	'	'
Cash and cash equivalents	326,730	365,245
Cash and cash equivalents, held for customers	1,332,399	1,190,880
Restricted Deposits, Fair Value Disclosure	9,120	'
Trading securities	633	'
Netting agreements	-54,614	-84
Total due to brokers	3,804	'
Total assets	1,672,686	1,556,125
Financial Liabilities:	'	'
Customer account liabilities	1,332,399	1,190,880
Netting agreements and cash collateral netting	-54,872	-84
Due to brokers total	182	'
Securities sold, not yet purchased	3,815	'
Follow-on Payment	'	3,672
Total liabilities	1,336,396	1,196,872
Fair Value, Measurements, Recurring | Exchange traded options	'	'
Financial Assets:	'	'
Total derivative assets	4,049	'
Financial Liabilities:	'	'
Total derivative liabilities	7,764	'
Fair Value, Measurements, Recurring | Futures contracts	'	'
Financial Assets:	'	'
Total derivative assets	54,369	0
Netting agreements	'	-84
Financial Liabilities:	'	'
Total derivative liabilities	47,060	'
Netting agreements and cash collateral netting	'	-84
Due to brokers total	'	2,320
Fair Value, Measurements, Recurring | Over the counter (OTC) options	'	'
Financial Liabilities:	'	'
Total derivative liabilities	1,457	'
Fair Value, Measurements, Recurring | Fair Value, Concentration of Credit Risk, Master Netting Arrangements [Member]	'	'
Financial Assets:	'	'
Netting agreements	-54,614	'
Financial Liabilities:	'	'
Netting agreements and cash collateral netting	-56,099	'
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level I)	'	'
Financial Assets:	'	'
Cash and cash equivalents	326,730	365,245
Cash and cash equivalents, held for customers	1,332,399	1,190,880
Restricted Deposits, Fair Value Disclosure	0	'
Trading securities	633	'
Total derivative assets	58,418	'
Total assets	1,718,180	1,556,209
Financial Liabilities:	'	'
Customer account liabilities	1,332,399	1,190,880
Total derivative liabilities	54,824	'
Securities sold, not yet purchased	3,815	'
Follow-on Payment	'	0
Total liabilities	1,391,038	1,193,284
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level I) | Exchange traded options	'	'
Financial Assets:	'	'
Total derivative assets	4,049	'
Financial Liabilities:	'	'
Total derivative liabilities	7,764	'
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level I) | Futures contracts	'	'
Financial Assets:	'	'
Total derivative assets	54,369	84
Financial Liabilities:	'	'
Total derivative liabilities	47,060	2,404
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level I) | Over the counter (OTC) options	'	'
Financial Liabilities:	'	'
Total derivative liabilities	0	'
Fair Value, Measurements, Recurring | Significant Observable Inputs (Level II)	'	'
Financial Assets:	'	'
Cash and cash equivalents	0	0
Cash and cash equivalents, held for customers	0	0
Restricted Deposits, Fair Value Disclosure	9,120	'
Trading securities	0	'
Total derivative assets	0	'
Total assets	9,120	0
Financial Liabilities:	'	'
Customer account liabilities	0	0
Total derivative liabilities	1,457	'
Securities sold, not yet purchased	0	'
Follow-on Payment	'	0
Total liabilities	1,457	0
Fair Value, Measurements, Recurring | Significant Observable Inputs (Level II) | Exchange traded options	'	'
Financial Assets:	'	'
Total derivative assets	0	'
Financial Liabilities:	'	'
Total derivative liabilities	0	'
Fair Value, Measurements, Recurring | Significant Observable Inputs (Level II) | Futures contracts	'	'
Financial Assets:	'	'
Total derivative assets	0	0
Financial Liabilities:	'	'
Total derivative liabilities	0	0
Fair Value, Measurements, Recurring | Significant Observable Inputs (Level II) | Over the counter (OTC) options	'	'
Financial Liabilities:	'	'
Total derivative liabilities	1,457	'
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level III)	'	'
Financial Assets:	'	'
Cash and cash equivalents	0	0
Cash and cash equivalents, held for customers	0	0
Restricted Deposits, Fair Value Disclosure	0	'
Trading securities	0	'
Total derivative assets	0	'
Total assets	0	0
Financial Liabilities:	'	'
Customer account liabilities	0	0
Total derivative liabilities	0	'
Securities sold, not yet purchased	0	'
Follow-on Payment	'	3,672
Total liabilities	0	3,672
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level III) | Exchange traded options	'	'
Financial Assets:	'	'
Total derivative assets	0	'
Financial Liabilities:	'	'
Total derivative liabilities	0	'
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level III) | Futures contracts	'	'
Financial Assets:	'	'
Total derivative assets	0	0
Financial Liabilities:	'	'
Total derivative liabilities	0	0
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level III) | Over the counter (OTC) options	'	'
Financial Liabilities:	'	'
Total derivative liabilities	$0	'

Fair_Value_Measurements_Fair_V1

Fair Value Measurements - Fair Value by Balance Sheet Groupings (Details) (USD $)	Sep. 30, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Quoted Prices in Active Markets for Identical Assets (Level I)	'	'
Financial Assets:	'	'
Due from brokers- unsettled spot FX	$0	$0
Due from brokers- unsettled common stock	0	'
Due from brokers - excess cash collateral	0	'
Equity method investments	0	0
Notes receivable	0	0
Exchange memberships	0	'
Total assets	0	0
Financial Liabilities:	'	'
Due to brokers- unsettled spot FX	0	0
Credit agreement	0	'
Notes payable	0	0
Senior convertible notes	0	0
Total liabilities	0	0
Significant Observable Inputs (Level II)	'	'
Financial Assets:	'	'
Due from brokers- unsettled spot FX	7,980	5,450
Due from brokers- unsettled common stock	3,730	'
Due from brokers - excess cash collateral	17,446	'
Equity method investments	0	0
Notes receivable	0	0
Exchange memberships	6,833	'
Total assets	35,989	5,450
Financial Liabilities:	'	'
Due to brokers- unsettled spot FX	734	6,332
Credit agreement	30,000	'
Notes payable	0	0
Senior convertible notes	149,909	149,418
Total liabilities	180,643	155,750
Significant Unobservable Inputs (Level III)	'	'
Financial Assets:	'	'
Due from brokers- unsettled spot FX	0	0
Due from brokers- unsettled common stock	0	'
Due from brokers - excess cash collateral	0	'
Equity method investments	17,199	13,504
Notes receivable	9,608	11,942
Exchange memberships	0	'
Total assets	26,807	25,446
Financial Liabilities:	'	'
Due to brokers- unsettled spot FX	0	0
Credit agreement	0	'
Notes payable	7,460	9,800
Senior convertible notes	0	0
Total liabilities	7,460	9,800
Carrying Value	'	'
Financial Assets:	'	'
Due from brokers- unsettled spot FX	7,980	5,450
Due from brokers- unsettled common stock	3,730	'
Due from brokers - excess cash collateral	17,446	'
Equity method investments	10,405	9,793
Notes receivable	9,608	11,942
Exchange memberships	6,429	'
Total assets	55,598	27,185
Financial Liabilities:	'	'
Due to brokers- unsettled spot FX	734	6,332
Credit agreement	30,000	'
Notes payable	7,460	9,800
Senior convertible notes	150,236	146,303
Total liabilities	188,430	162,435
Fair Value	'	'
Financial Assets:	'	'
Due from brokers- unsettled spot FX	7,980	5,450
Due from brokers- unsettled common stock	3,730	'
Due from brokers - excess cash collateral	17,446	'
Equity method investments	17,199	13,504
Notes receivable	9,608	11,942
Exchange memberships	6,833	'
Total assets	62,796	30,896
Financial Liabilities:	'	'
Due to brokers- unsettled spot FX	734	6,332
Credit agreement	30,000	'
Notes payable	7,460	9,800
Senior convertible notes	149,909	149,418
Total liabilities	$188,103	$165,550

Fair_Value_Measurements_Signif

Fair Value Measurements - Significant Unobservable Inputs Reconciliation (Details) (USD $)	9 Months Ended	12 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]	'	'
Beginning Balance	$3,672	$0
Additions	0	10,631
Net Unrealized / Realized (Gains) Losses	-3,672	-6,959
Total	0	3,672
Follow-on Payment	'	'
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]	'	'
Beginning Balance	3,672	0
Additions	0	10,631
Net Unrealized / Realized (Gains) Losses	-3,672	-6,959
Total	$0	$3,672

Derivative_Financial_Instrumen2

Derivative Financial Instruments (Detail) (USD $)	Sep. 30, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Derivatives Assets	'	'
Total derivative assets	$58,418	$84
Netting agreements	-54,614	-84
Total derivative assets	3,804	0
Notional	3,471,144	19,475
Derivative Liabilities	'	'
Total derivative liabilities	56,281	2,404
Netting agreements and cash collateral netting	-56,099	-84
Total derivative liabilities	182	2,320
Total	3,622	-2,320
Notional	609,357	140,429
Derivative, notional amount	4,080,501	159,904
Exchange traded options	'	'
Derivatives Assets	'	'
Total derivative assets	4,049	'
Notional	117,046	'
Derivative Liabilities	'	'
Total derivative liabilities	7,764	'
Notional	100,353	'
Futures contracts	'	'
Derivatives Assets	'	'
Total derivative assets	54,369	'
Notional	3,354,098	'
Derivative Liabilities	'	'
Total derivative liabilities	47,060	'
Notional	507,547	'
OTC options	'	'
Derivative Liabilities	'	'
Total derivative liabilities	1,457	'
Notional	$1,457	'

Derivative_Financial_Instrumen3

Derivative Financial Instruments - Additional Information (Detail) (USD $)	3 Months Ended		9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Derivative Instruments, Gain (Loss) [Line Items]	'	'	'	'
Gains (Losses)	($27,873)	$355	$6,180	$1,752
Exchange traded options	'	'	'	'
Derivative Instruments, Gain (Loss) [Line Items]	'	'	'	'
Gains (Losses)	-5,915	'	14,002	'
Futures contracts	'	'	'	'
Derivative Instruments, Gain (Loss) [Line Items]	'	'	'	'
Gains (Losses)	-21,181	355	-7,428	1,752
Over the counter (OTC) options	'	'	'	'
Derivative Instruments, Gain (Loss) [Line Items]	'	'	'	'
Gains (Losses)	-777	'	-394	'
Retail Trading	'	'	'	'
Derivative Instruments, Gain (Loss) [Line Items]	'	'	'	'
Gains (Losses)	-33,031	-4,192	-12,227	-13,958
Retail Trading | Exchange traded options	'	'	'	'
Derivative Instruments, Gain (Loss) [Line Items]	'	'	'	'
Gains (Losses)	0	'	0	'
Retail Trading | Futures contracts	'	'	'	'
Derivative Instruments, Gain (Loss) [Line Items]	'	'	'	'
Gains (Losses)	-33,031	-4,192	-12,227	-13,958
Retail Trading | Over the counter (OTC) options	'	'	'	'
Derivative Instruments, Gain (Loss) [Line Items]	'	'	'	'
Gains (Losses)	0	'	0	'
Institutional Trading	'	'	'	'
Derivative Instruments, Gain (Loss) [Line Items]	'	'	'	'
Gains (Losses)	5,158	4,547	18,407	15,710
Institutional Trading | Exchange traded options	'	'	'	'
Derivative Instruments, Gain (Loss) [Line Items]	'	'	'	'
Gains (Losses)	-5,915	'	14,002	'
Institutional Trading | Futures contracts	'	'	'	'
Derivative Instruments, Gain (Loss) [Line Items]	'	'	'	'
Gains (Losses)	11,850	4,547	4,799	15,710
Institutional Trading | Over the counter (OTC) options	'	'	'	'
Derivative Instruments, Gain (Loss) [Line Items]	'	'	'	'
Gains (Losses)	($777)	'	($394)	'

Income_Taxes_Additional_Inform

Income Taxes - Additional Information (Detail)	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Income Tax Disclosure [Abstract]	'	'	'	'
Effective tax rate	29.30%	-38.50%	-182.70%	36.30%

Segments_Companys_Operations_b

Segments - Company's Operations by Reportable Segment (Detail) (USD $)	3 Months Ended		9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
			geographic_area
			Segment
Segment Reporting Information [Line Items]	'	'	'	'
Number of operating segments	'	'	2	'
Number of geographic areas	'	'	3	'
Total revenues	$116,147	$113,248	$329,082	$376,245
Total expenses	111,867	119,406	329,074	329,285
Loss on equity method investments	376	183	910	728
Income (loss) before income taxes	3,904	-6,341	-902	46,232
Operating Segments | Retail Trading	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'
Total revenues	91,861	90,392	252,866	294,041
Total expenses	52,284	56,900	156,122	166,332
Loss on equity method investments	0	0	0	0
Income (loss) before income taxes	39,577	33,492	96,744	127,709
Operating Segments | Institutional Trading	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'
Total revenues	23,926	22,856	75,856	82,204
Total expenses	27,859	20,721	81,049	73,636
Loss on equity method investments	239	244	606	689
Income (loss) before income taxes	-4,172	1,891	-5,799	7,879
Corporate	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'
Total revenues	360	0	360	0
Total expenses	31,724	41,785	91,903	89,317
Loss on equity method investments	137	-61	304	39
Income (loss) before income taxes	($31,501)	($41,724)	($91,847)	($89,356)

Segments_Assets_by_Reportable_

Segments - Assets by Reportable Segment (Detail) (USD $)	Sep. 30, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Segment Reporting Information [Line Items]	'	'
Total assets	$2,384,409	$2,223,947
Corporate	'	'
Segment Reporting Information [Line Items]	'	'
Total assets	191,154	183,626
Operating Segments | Retail Trading	'	'
Segment Reporting Information [Line Items]	'	'
Total assets	1,738,368	1,622,829
Operating Segments | Institutional	'	'
Segment Reporting Information [Line Items]	'	'
Total assets	$454,887	$417,492

Subsequent_Events_Additional_I

Subsequent Events - Additional Information (Detail) (Subsequent Event, Common Class A, USD $)	Nov. 06, 2014
Subsequent Event | Common Class A	'
Subsequent Event [Line Items]	'
Dividend declared (in dollars per share)	$0.06