Related Party Transactions - Additional Information (Detail)																	1 Months Ended			3 Months Ended				6 Months Ended		12 Months Ended
	Jun. 30, 2016 USD ($) $ / shares shares	May 27, 2016 USD ($)	Mar. 09, 2016 $ / shares shares	Feb. 28, 2016 shares	Feb. 24, 2016 $ / shares shares	Feb. 23, 2016 $ / shares shares	Jan. 15, 2016 USD ($)	Nov. 04, 2015 USD ($) shares	Jul. 27, 2015 $ / shares shares	Jun. 05, 2015 shares	Apr. 13, 2015 $ / shares shares	Jan. 30, 2015 $ / shares shares	Jan. 01, 2015 USD ($) shares	Jun. 03, 2014 USD ($) shares	Oct. 29, 2013	Apr. 01, 2010 USD ($)	Jun. 30, 2016 USD ($) $ / shares shares	May 31, 2016 $ / shares shares	Apr. 30, 2016 $ / shares shares	Jun. 30, 2016 USD ($) $ / shares shares	Mar. 31, 2016 $ / shares shares	Jun. 30, 2015 USD ($) $ / shares shares	Mar. 31, 2015 USD ($)	Jun. 30, 2016 USD ($) $ / shares shares	Jun. 30, 2015 USD ($) $ / shares shares	Dec. 31, 2015 USD ($) $ / shares shares	Aug. 04, 2016 USD ($)	Oct. 27, 2015 USD ($)	Oct. 01, 2015 USD ($)	Jun. 23, 2015 USD ($)	Aug. 31, 2013 USD ($)
Related Party Transactions [Abstract]
Recognized related party revenues | $																				$ 4,865,000		$ 6,095,000		$ 11,935,000	$ 12,701,000
Purchase of equity method investments | $																								7,612,000	687,000
Commissions | $																				498,588,000		487,810,000		973,675,000	903,093,000
Interest expense | $																				14,624,000		18,439,000		28,082,000	34,341,000
Payables to Cantor related to open derivative contracts | $	$ 23,650,000																$ 23,650,000			23,650,000				23,650,000		$ 21,551,000
Employee loans | $	247,922,000																$ 247,922,000			247,922,000				$ 247,922,000		158,176,000
Repurchases, Number of Shares																	245,824	291,323	260,042		7,187,046			7,984,235
Average price per share of common stock repurchased | $ / shares																	$ 9.17	$ 8.87	$ 9.10		$ 8.72			$ 8.75
Aggregate proceeds from issuance of common stock | $																								$ 14,961,000
Related party service fee															10.00%
Professional and consulting fees | $																				14,201,000		15,220,000		$ 29,611,000	38,501,000
Limited partnership units exchange ratio																								1
Partnership unit repurchase price description																								Repurchased by the Company at the average price of shares of Class A common stock sold under the Company's controlled equity offering less 2%, or $91,558.
Redemption of limited partnership units					0
Employee stock option exercised, shares																								250,000
Employee stock option exercise price per share | $ / shares																								$ 0
Principal sum of loan due from related parties | $	8,231,000																$ 8,231,000			8,231,000				$ 8,231,000		$ 15,466,000
Aqua [Member]
Related Party Transactions [Abstract]
Purchase of equity method investments | $																						$ 500,000			$ 700,000
Increase in authorization amount for loans and investments, other credit support arrangements | $																												$ 4,000,000
Authorization amount for loans and investments, other credit support arrangements | $																												$ 16,200,000
Principal sum of loan due from related parties | $	$ 980,000																$ 980,000			$ 980,000				$ 980,000
Maturity date of subordinated loan																								Sep. 01, 2017
Loan Receivable, Description of Variable Rate Basis																								Three month LIBOR plus 600 basis points
Loan Receivable, Basis Spread on Variable Rate	600.00%																600.00%			600.00%				600.00%
Class A Common Stock [Member]
Related Party Transactions [Abstract]
Convertible Notes, shares																										24,042,599
Common stock, par value | $ / shares	$ 0.01																$ 0.01			$ 0.01				$ 0.01		$ 0.01
Repurchases, Number of Shares																				797,189		6,520		7,984,235	741,081	1,416,991
Average price per share of common stock repurchased | $ / shares					$ 8.40							$ 7.83								$ 9.04		$ 6.29		$ 8.75	$ 7.94
Common stock, shares issued																								1,690,305		129,151
Cantor purchase of Cantor units from BGC Holdings upon redemption of founding/working partner units and subsequent repurchases by BGC Holdings, units																										1,775,481
Repurchase of partnership interests | $													$ 91,558
Percentage difference between purchase price of partnership unit and average price of common stock													2.00%
Redemption of limited partnership units												0
Shares held by executive officers					612,958							598,904
Partnership units received by related parties												87,140
Class B Units [Member] | LFI [Member]
Related Party Transactions [Abstract]
Purchase of LFI units														1,000
Investment ownership percentage amount							20.00%							10.00%
Investment in equity amount | $														$ 6,500,000
Option to purchase additional units														1,000
Additional investment in investment in equity | $														$ 6,500,000
Purchase of equity method investments | $							$ 6,500,000
Class B Common Stock [Member]
Related Party Transactions [Abstract]
Common stock, par value | $ / shares	$ 0.01																$ 0.01			$ 0.01				$ 0.01		$ 0.01
Common stock, shares issued																				0		0		0	0
Mr. Lutnick [Member]
Related Party Transactions [Abstract]
Number of new partnership units converted												1,000,000	1,000,000
Grant of new class of partnership units					1,500,000							4,000,000
Conversion percentage of new partnership units												25.00%
Shares held by executive officers				235,357
Partnership units non-exchangeable shares granted				2,127,648
Mr. Lutnick [Member] | Class A Common Stock [Member]
Related Party Transactions [Abstract]
Employee stock option exercised, shares			250,000
Employee stock option exercise price per share | $ / shares			$ 8.42
Number of shares issued as a result of stock option exercise			17,403
Mr. Lutnick [Member] | Partnership Units [Member]
Related Party Transactions [Abstract]
Number of new partnership units converted													550,000
Number of partnership units exchangeable for shares and cash													239,739
Partnership units non-exchangeable shares granted					750,000
Mr. Lutnick [Member] | PPSUs [Member]
Related Party Transactions [Abstract]
Number of new partnership units converted													450,000
Number of partnership units exchangeable for shares and cash													196,150
Partnership units non-exchangeable shares granted					291,667
Mr. Merkel [Member]
Related Party Transactions [Abstract]
Number of new partnership units converted													142,857
Grant of new class of partnership units					1,000,000
Mr. Merkel [Member] | Class A Common Stock [Member]
Related Party Transactions [Abstract]
Repurchases, Number of Shares					120,000
Shares held by executive officers					150,382							16,354
Mr. Merkel [Member] | Partnership Units [Member]
Related Party Transactions [Abstract]
Number of new partnership units converted													78,571
Number of partnership units exchangeable for shares and cash													5,607
Stock issued to executive officer									8,536
Partnership units repurchased from executive officer									8,536
Partnership units repurchased from executive officer, per share | $ / shares									$ 8.34
Partnership units non-exchangeable shares granted					114,583
Mr. Merkel [Member] | PPSUs [Member]
Related Party Transactions [Abstract]
Number of new partnership units converted													64,286
Number of partnership units exchangeable for shares and cash													4,588
Stock issued to executive officer									6,983
Partnership units repurchased from executive officer									6,983
Partnership units repurchased from executive officer, per share | $ / shares									$ 9.15
Partnership units non-exchangeable shares granted					93,750
Mr. Lynn [Member]
Related Party Transactions [Abstract]
Number of new partnership units converted												250,000
Grant of new class of partnership units					2,000,000							1,000,000
Conversion percentage of new partnership units												25.00%
Redemption of limited partnership units												0
Percentage of limited partnership units deemed redemption												9.75%
Mr. Lynn [Member] | Class A Common Stock [Member]
Related Party Transactions [Abstract]
Shares held by executive officers					431,782							455,733
Partnership units received by related parties					64,787							68,381
Mr. Lynn [Member] | Limited Partnership Units [Member]
Related Party Transactions [Abstract]
Partnership units non-exchangeable shares granted					621,429
Mr. Lynn [Member] | PLPUs [Member]
Related Party Transactions [Abstract]
Partnership units non-exchangeable shares granted					241,667
Mr. Windeatt [Member]
Related Party Transactions [Abstract]
Grant of new class of partnership units					75,000
Mr. Windeatt [Member] | Class A Common Stock [Member]
Related Party Transactions [Abstract]
Shares held by executive officers												95,148
Partnership units received by related parties												20,684
Mr. Windeatt [Member] | Limited Partnership Units [Member]
Related Party Transactions [Abstract]
Partnership units non-exchangeable shares granted					105,188
Mr. Windeatt [Member] | PLPUs [Member]
Related Party Transactions [Abstract]
Partnership units non-exchangeable shares granted					40,906
Mr. Sadler [Member] | Class A Common Stock [Member]
Related Party Transactions [Abstract]
Shares held by executive officers					30,794							31,669
Partnership units received by related parties					4,621							4,752
Mr. Sadler [Member] | Limited Partnership Units [Member]
Related Party Transactions [Abstract]
Partnership units non-exchangeable shares granted					55,688
Mr. Sadler [Member] | PLPUs [Member]
Related Party Transactions [Abstract]
Partnership units non-exchangeable shares granted					21,656
Partnership N [Member]
Related Party Transactions [Abstract]
Conversion percentage of new partnership units					25.00%
8.75% Convertible Notes [Member]
Related Party Transactions [Abstract]
Principal amount of debt component | $																$ 150,000,000
Stated interest rate																8.75%						8.75%			8.75%
Senior Notes maturity date																								Apr. 15, 2015
Interest expense recorded on Senior Notes | $																						$ 500,000			$ 3,800,000
8.75% Convertible Notes [Member] | Class A Common Stock [Member]
Related Party Transactions [Abstract]
Convertible Notes, shares																						24,042,599			24,042,599
5.125% Senior Notes [Member]
Related Party Transactions [Abstract]
Principal amount of debt component | $		$ 300,000,000
Debt instrument maturity year																								2021
Stated interest rate	5.125%	5.125%															5.125%			5.125%				5.125%		5.125%
Senior Notes maturity date																								May 27, 2021
Interest expense recorded on Senior Notes | $																				$ 1,600,000				$ 1,600,000
Cantor [Member]
Related Party Transactions [Abstract]
Mark-up cost of services																								7.50%
Company ownership of Tower Bridge																								52.00%
Cantor ownership of Tower Bridge	48.00%																48.00%			48.00%				48.00%
Recognition of share of foreign exchange gains (losses) | $																				$ (1,500,000)		$ (25,000)		$ (1,400,000)	$ 621,000
Commissions | $																				28,000		140,000		80,000	204,000
Investment in asset-backed commercial paper program | $	$ 0																$ 0			0				0		$ 0
Investment authorization in asset-backed commercial paper program | $																															$ 350,000,000
Professional and consulting fees | $																				$ 0		0		$ 0	0
Debt due to Cantor | $								$ 46,289
Cantor [Member] | Aqua [Member]
Related Party Transactions [Abstract]
Investment ownership percentage amount	49.00%																49.00%			49.00%				49.00%
Purchase of equity method investments | $																				$ 800,000				$ 1,100,000
Investment ownership percentage	51.00%																51.00%			51.00%				51.00%
Cantor [Member] | Class A Common Stock [Member]
Related Party Transactions [Abstract]
Repurchases, Number of Shares						5,000,000
Average price per share of common stock repurchased | $ / shares						$ 8.72
Cantor [Member] | Revolving Credit Facility [Member]
Related Party Transactions [Abstract]
Debt Instrument, description																								The outstanding balances would bear interest at the higher of the borrower's or the lender's short-term borrowing rate then in effect, plus 1%.
Borrowings outstanding under the Credit Agreement | $	$ 0																$ 0			$ 0				$ 0
Line of credit facility, borrowing amount | $																													$ 100,000,000
Interest expense | $																										0
Cantor [Member] | Maximum [Member] | Revolving Credit Facility [Member]
Related Party Transactions [Abstract]
Principal amount of debt component | $																														$ 150,000,000
Cantor [Member] | 8.75% Convertible Notes [Member]
Related Party Transactions [Abstract]
Principal amount of debt component | $																$ 150,000,000
Repayment of Senior Notes | $																$ 150,000,000
Debt instrument maturity year																2015
Convertible Notes issuance date																								Apr. 01, 2010
Stated interest rate																8.75%
Senior Notes maturity date																								Apr. 01, 2010
Interest expense recorded on Senior Notes | $																						500,000			3,800,000
CF & Co [Member]
Related Party Transactions [Abstract]
Advisory fees payable | $																							$ 7,100,000
CF & Co [Member] | Sale of Trayport [Member]
Related Party Transactions [Abstract]
Advisory fees payable | $																										$ 5,100,000
CF & Co [Member] | November 2014 Sales Agreement [Member]
Related Party Transactions [Abstract]
Common stock, shares issued																				3,300,000				3,700,000
Aggregate proceeds from issuance of common stock | $																				$ 30,300,000				$ 33,600,000
Weighted-average price per share | $ / shares																				$ 9.18				$ 9.16
Related party expenses | $																				$ 600,000		200,000		$ 700,000	500,000
CF & Co [Member] | Maximum [Member]
Related Party Transactions [Abstract]
Stated interest rate																										1.00%
CF & Co [Member] | 8.75% Convertible Notes [Member] | Class A Common Stock [Member]
Related Party Transactions [Abstract]
Convertible Notes, shares											24,042,599
Stated interest rate											8.75%
Senior Notes maturity date																								Apr. 15, 2015
Common stock, par value | $ / shares											$ 0.01
Debt Instrument, covenant description																								On June 15, 2015, the Company filed a resale registration statement on Form S-3 pursuant to which 24,042,599 shares of Class A common stock may be sold from time to time by Cantor or by certain of its pledgees, donees, distributees, counterparties, transferees or other successors of interest of the shares, including banks or other financial institutions which may enter into stock pledge, stock loan or other financing transactions with Cantor or its affiliates, as well as by their respective pledgees, donees, distributees, counterparties, transferees or other successors in interest.
CF & Co [Member] | 5.125% Senior Notes [Member] | Underwriting Fees [Member]
Related Party Transactions [Abstract]
Underwriting fees | $		$ 500,000
Purchased senior notes | $		15,000,000
Relief Fund [Member]
Related Party Transactions [Abstract]
Interest-free loan to related party | $																										$ 1,000,000
Promissory note repayment date																								Aug. 04, 2016
Relief Fund [Member] | Scenario, Forecast [Member]
Related Party Transactions [Abstract]
Promissory note from related party | $																											$ 1,000,000
Relief Fund [Member] | Accounts Payable, Accrued and Other Liabilities [Member]
Related Party Transactions [Abstract]
Charitable contributions | $	38,000,000																38,000,000			38,000,000				$ 38,000,000
Relief Fund [Member] | Other Expenses [Member]
Related Party Transactions [Abstract]
Charitable contributions | $																										40,000,000
Cantor Fitzgerald Relief Fund [Member] | Class A Common Stock [Member]
Related Party Transactions [Abstract]
Repurchases, Number of Shares						970,639
Average price per share of common stock repurchased | $ / shares						$ 8.72
Cantor Rights to Purchase Exchangeable Units [Member]
Related Party Transactions [Abstract]
Limited partnership units exchange ratio								1
Cantor purchase of Cantor units from BGC Holdings upon redemption of founding/working partner units and subsequent repurchases by BGC Holdings, units								1,775,481
Aggregate consideration of non-exchangeable founding/working partner units redeemed | $								$ 2,296,801
Number of non-exchangeable founding/working partner units redeemed								588,356
Aggregate exchangeable limited partnership units purchased								554,196
Aggregate consideration amount | $								$ 2,115,306
Cantor Rights to Purchase Exchangeable Units [Member] | Exchange Rights [Member]
Related Party Transactions [Abstract]
Aggregate exchangeable limited partnership units purchased								1,221,285
Aggregate consideration amount | $								$ 4,457,436
Cantor Rights to Purchase Exchangeable Units [Member] | Maximum [Member]
Related Party Transactions [Abstract]
Number of shares, right to exchange from Class A to Class B common stock																								34,649,693
Cantor and ELX [Member]
Related Party Transactions [Abstract]
Recognized related party revenues | $																				4,900,000		6,100,000		$ 11,900,000	12,700,000
Service charges | $																				9,700,000		10,500,000		22,600,000	21,400,000
Compensation to leased employees | $																				6,200,000		6,400,000		12,900,000	12,700,000
Cantor's share of net profit in Tower Bridge | $																				100,000		300,000		500,000	1,000,000
CF Group Management, Inc [Member]
Related Party Transactions [Abstract]
Number of shares, right to exchange from Class A to Class B common stock										34,649,693
Cantor and Freedom International Brokerage [Member]
Related Party Transactions [Abstract]
Receivables from Freedom International Brokerage | $	4,700,000																4,700,000			4,700,000				4,700,000		4,100,000
Receivables from Cantor related to open derivative contracts | $	200,000																200,000			200,000				200,000		900,000
Payables to Cantor related to open derivative contracts | $	11,000																11,000			11,000				11,000		400,000
Payables to Cantor related to pending equity trades | $	0																0			0				0		4,600,000
Employee Loans [Member]
Related Party Transactions [Abstract]
Employee loans | $	$ 247,900,000																$ 247,900,000			247,900,000				247,900,000		$ 158,200,000
Compensation expense related to employee loans | $																				10,500,000		11,700,000		21,000,000	19,800,000
CastleOak Securities LP [Member] | 5.125% Senior Notes [Member] | Underwriting Fees [Member]
Related Party Transactions [Abstract]
Underwriting fees | $		$ 18,000
CCRE [Member]
Related Party Transactions [Abstract]
Recognized related party revenues | $																				$ 900,000		$ 100,000		$ 1,800,000	$ 200,000
Cantor And CFGM [Member] | Class A Common Stock [Member]
Related Party Transactions [Abstract]
Convertible Notes, shares	17,014,511										24,042,599
Cantor And CFGM [Member] | Class B Common Stock [Member]
Related Party Transactions [Abstract]
Number of shares, right to exchange from Class A to Class B common stock																								34,649,693