Related Party Transactions - Additional Information (Detail)																													3 Months Ended				12 Months Ended
	Dec. 31, 2016 USD ($) $ / shares shares	Dec. 14, 2016 USD ($)	Nov. 16, 2016 $ / shares shares	Nov. 11, 2016 $ / shares shares	Nov. 10, 2016 $ / shares shares	Nov. 07, 2016 USD ($) shares	Oct. 25, 2016 shares	Sep. 30, 2016 $ / shares shares	Aug. 16, 2016 $ / 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	Feb. 09, 2016 USD ($)	Jan. 15, 2016 USD ($)	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 ($) shares	Jul. 21, 2014 USD ($) shares	Jun. 03, 2014 USD ($) shares	Feb. 05, 2014 $ / shares shares	Jan. 21, 2014 $ / shares shares	Oct. 29, 2013	Apr. 01, 2010 USD ($)	Dec. 31, 2016 USD ($) $ / shares shares	Sep. 30, 2016 $ / shares shares	Jun. 30, 2016 $ / shares shares	Mar. 31, 2016 $ / shares shares	Dec. 31, 2016 USD ($) $ / shares shares	Dec. 31, 2015 USD ($) $ / shares shares	Dec. 31, 2014 USD ($) $ / shares shares	Nov. 04, 2016	Aug. 04, 2016 USD ($)	Jul. 31, 2016 USD ($)	Oct. 27, 2015 USD ($)	Oct. 01, 2015 USD ($)	Jun. 23, 2015 USD ($)	Dec. 09, 2014 USD ($)	Aug. 31, 2013 USD ($)
Related Party Transactions [Abstract]
Recognized related party revenues | $																																	$ 24,200,000	$ 25,348,000	$ 28,379,000
Equity investment | $																																	1,235,000	1,268,000	892,000
Commissions | $																																	1,994,227,000	1,931,860,000	1,307,912,000
Interest expense | $																																	57,637,000	69,359,000	37,945,000
Reverse purchase agreement outstanding | $	$ 54,659,000																												$ 54,659,000				54,659,000	0
Payables to Cantor related to open derivative contracts | $	28,976,000																												28,976,000				28,976,000	22,470,000
Employee loans | $	267,527,000																												$ 267,527,000				267,527,000	158,194,000
Interest income | $																																	$ 12,271,000	10,643,000	7,313,000
Repurchase of Class A common stock																													1,497,760	1,341,947	797,189	7,187,046	10,823,942
Average price per share of common stock repurchased | $ / shares																													$ 9.59	$ 8.90	$ 9.04	$ 8.72	$ 8.88
Aggregate proceeds from issuance of common stock | $																																	$ 15,280,000
Securities loaned | $	$ 0																												$ 0				0	117,890,000
Related party service fee																											10.00%
Professional and consulting fees | $																																	60,920,000	66,382,000	52,598,000
Payments of referrals for leasing or other services | $																																	$ 23,864,000	$ 18,755,000	$ 12,623,000
Limited partnership units exchange ratio																																	1
Founding partner units remaining	650,364																												650,364				650,364
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																																	1,057,534	94,000
Employee stock option exercise price per share | $ / shares																																	$ 0	$ 0	$ 0
Repurchases value of shares | $	$ 288,743,000																												$ 288,743,000				$ 288,743,000	$ 212,331,000
Principal sum of loan due from related parties | $	6,967,000																												6,967,000				6,967,000	9,050,000
Market Value [Member]
Related Party Transactions [Abstract]
Reverse purchase agreement outstanding | $	$ 54,700,000																												$ 54,700,000				$ 54,700,000
Aqua [Member]
Related Party Transactions [Abstract]
Investment ownership percentage amount	49.00%																												49.00%				49.00%
Equity investment | $																																	$ 1,200,000	$ 1,300,000
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
Maturity date of subordinated loan																																	Sep. 01, 2018
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%
Class A Common Stock [Member]
Related Party Transactions [Abstract]
Convertible Notes, shares																																	6,909	24,042,599
Common stock, par value | $ / shares	$ 0.01																												$ 0.01				$ 0.01	$ 0.01
Repurchase of Class A common stock																									636,841								10,823,942	1,416,991	13,630,725
Average price per share of common stock repurchased | $ / shares													$ 8.40								$ 7.83				$ 6.51	$ 6.51							$ 8.88	$ 8.55
Common stock, shares issued																																	2,004,533	129,151	47,896
Previously-owned common stock purchased	244,870,000																												244,870,000				244,870,000	219,063,000
Cantor purchase of Cantor units from BGC Holdings upon redemption of founding/working partner units and subsequent repurchases by BGC Holdings, units																																	624,762	1,775,481	3,142,257
Shares held by executive officers													612,958								598,904					1,254,723
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
Partnership units received by related parties																					87,410
Employee stock option exercised, shares																																	76,000	84,421
Class B Units [Member] | Lucera [Member]
Related Party Transactions [Abstract]
Purchase of LFI units							9,000																	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
Equity investment | $																$ 6,500,000
Percentage of outstanding common stock owned by parent																																				100.00%
Class B Common Stock [Member]
Related Party Transactions [Abstract]
Common stock, par value | $ / shares	$ 0.01																												$ 0.01				$ 0.01	$ 0.01
Common stock, shares issued																																	0	0
Previously-owned common stock purchased	34,848,000																												34,848,000				34,848,000	34,848,000
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
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]
Repurchase of Class A common stock																									424,347
Shares held by executive officers													431,782								455,733					424,347
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. Merkel [Member]
Related Party Transactions [Abstract]
Number of new partnership units converted																						142,857
Grant of new class of partnership units													1,000,000								1,000,000
Mr. Merkel [Member] | Class A Common Stock [Member]
Related Party Transactions [Abstract]
Repurchase of Class A common stock								16,634					120,000												14,689
Average price per share of common stock repurchased | $ / shares								$ 8.75
Shares held by executive officers													150,382								16,354					14,689
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. 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]
Repurchase of Class A common stock																									157,833
Shares held by executive officers																					95,148					146,843
Partnership units received by related parties																					14,277
Mr. Windeatt [Member] | Class A Common Stock [Member] | Restricted Shares [Member]
Related Party Transactions [Abstract]
Repurchase of Class A common stock																									146,843
Mr. Windeatt [Member] | Class A Common Stock [Member] | Freely Tradable Shares [Member]
Related Party Transactions [Abstract]
Repurchase of Class A common stock																									10,990
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]
Repurchase of Class A common stock																									39,972
Shares held by executive officers													30,794								31,669					39,972
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
Mr. Lutnick [Member]
Related Party Transactions [Abstract]
Shares held by executive officers												235,357
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%
Partnership units non-exchangeable shares granted												2,127,648
Mr. Lutnick [Member] | Class A Common Stock [Member]
Related Party Transactions [Abstract]
Repurchase of Class A common stock									36,405
Average price per share of common stock repurchased | $ / shares									$ 8.77
Shares held by executive officers																										628,872
Employee stock option exercised, shares				800,000							250,000
Employee stock option exercise price per share | $ / shares				$ 8.80							$ 8.42
Number of shares issued as a result of stock option exercise				51,064							17,403
Repurchases value of shares | $																																						$ 350,000
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
Partnership N [Member]
Related Party Transactions [Abstract]
Conversion percentage of new partnership units													25.00%
Trusts For Benefit of Merkel's Immediate Family [Member] | Class A Common Stock [Member]
Related Party Transactions [Abstract]
Repurchase of Class A common stock								4,131
Mr. Dalton [Member] | Class A Common Stock [Member]
Related Party Transactions [Abstract]
Employee stock option exercised, shares					7,534
Employee stock option exercise price per share | $ / shares					$ 8.87
Minimum [Member]
Related Party Transactions [Abstract]
Minimum gross revenue required | $		$ 5,000,000
8.75% Convertible Notes [Member]
Related Party Transactions [Abstract]
Principal amount of debt component | $																												$ 150,000,000
Stated interest rate																												8.75%						8.75%
Senior Notes maturity date																																	Apr. 15, 2015
Interest expense recorded on Senior Notes | $																																	$ 0	$ 3,800,000	$ 13,100,000
8.75% Convertible Notes [Member] | Class A Common Stock [Member]
Related Party Transactions [Abstract]
Convertible Notes, shares																																		24,042,599
5.375% Senior Notes [Member]
Related Party Transactions [Abstract]
Principal amount of debt component | $	$ 300,000,000																												$ 300,000,000				$ 300,000,000									$ 300,000,000
Debt instrument maturity year																																	2019
Stated interest rate	5.375%																												5.375%				5.375%	5.375%								5.375%
Senior Notes maturity date																																	Dec. 09, 2019
Interest expense recorded on Senior Notes | $																																	$ 17,100,000	$ 17,100,000	1,000,000
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%
Senior Notes maturity date																																	May 27, 2021
Interest expense recorded on Senior Notes | $																																	$ 9,600,000	$ 0	0
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%
Recognition of share of foreign exchange gains (losses) | $																																	$ 4,200,000	(496,000)	934,000
Commissions | $																																	100,000	300,000	400,000
Investment in asset-backed commercial paper program | $	$ 0																												$ 0				0	0
Investment authorization in asset-backed commercial paper program | $																																											$ 350,000,000
Reverse purchase agreement outstanding | $	$ 54,700,000																												$ 54,700,000				54,700,000	0
Professional and consulting fees | $																																	$ 0	0	0
Debt due to Cantor | $																	$ 46,289
Cantor [Member] | Aqua [Member]
Related Party Transactions [Abstract]
Investment ownership percentage	51.00%																												51.00%				51.00%
Cantor [Member] | Lucera [Member]
Related Party Transactions [Abstract]
Recognized related party revenues | $																																	$ 2,900,000	2,500,000	1,300,000
Related party capital contributions | $																																	15,000,000	0	12,200,000
Cantor [Member] | Class A Common Stock [Member]
Related Party Transactions [Abstract]
Repurchase of Class A common stock														5,000,000
Average price per share of common stock repurchased | $ / shares														$ 8.72
Cantor [Member] | Class B Units [Member] | Lucera [Member]
Related Party Transactions [Abstract]
Equity investment | $																																	24,200,000
Post-closing adjustment | $																																	4,800,000
Cantor [Member] | Audit Committee [Member]
Related Party Transactions [Abstract]
Development expenses | $																																	$ 1,200,000
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
Line of credit facility, borrowing amount | $																																								$ 100,000,000
Interest expense | $																																	$ 0	800,000
Cantor [Member] | Maximum [Member] | Audit Committee [Member]
Related Party Transactions [Abstract]
Development expenses | $															$ 1,400,000
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 | $																																		3,800,000	13,100,000
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
CF & Co [Member]
Related Party Transactions [Abstract]
Securities loaned | $	0																												0				$ 0	117,900,000
Advisory fees payable | $																																		7,100,000
Guarantee fees | $																																	$ 125,000	188,542	0
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																																	7,600,000	6,900,000
Aggregate proceeds from issuance of common stock | $																																	$ 70,400,000	$ 62,400,000
Weighted-average price per share | $ / shares																																	$ 9.28	$ 9.07
Related party expenses | $																																	$ 1,400,000	$ 1,200,000	1,300,000
CF & Co [Member] | Market Value [Member]
Related Party Transactions [Abstract]
Securities loaned | $																																		$ 116,300,000
CF & Co [Member] | Underwriting Fees [Member]
Related Party Transactions [Abstract]
Underwriting fees | $																																			252,000
CF & Co [Member] | Maximum [Member]
Related Party Transactions [Abstract]
Stated interest rate																																		1.00%
CF & Co [Member] | Minimum [Member]
Related Party Transactions [Abstract]
Stated interest rate																																		0.80%
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 in 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
CastleOak Securities LP [Member] | 5.125% Senior Notes [Member] | Underwriting Fees [Member]
Related Party Transactions [Abstract]
Underwriting fees | $										$ 18,000
Cantor Rights to Purchase Exchangeable Units [Member]
Related Party Transactions [Abstract]
Limited partnership units exchange ratio																	1
Aggregate exchangeable limited partnership units purchased						141,523											554,196
Number of non-exchangeable founding/working partner units redeemed						141,523											588,356						1,371,058
Founding partner units remaining for which Cantor has the right to purchase Cantor units																							1,771,199
Aggregate consideration amount | $						$ 560,190											$ 2,115,306						$ 10,600,000
Aggregate purchase of units and shares																							5,000,000
Number of units purchased from related party																							3,142,257
Cantor purchase of Cantor units from BGC Holdings upon redemption of founding/working partner units and subsequent repurchases by BGC Holdings, units						624,762											1,775,481
Aggregate consideration of non-exchangeable founding/working partner units redeemed | $						$ 560,190											$ 2,296,801
Founding partner units remaining						548,259
Cantor Rights to Purchase Exchangeable Units [Member] | Exchange Rights [Member]
Related Party Transactions [Abstract]
Aggregate exchangeable limited partnership units purchased						483,239											1,221,285						3,142,257
Aggregate consideration amount | $						$ 1,796,367											$ 4,457,436
Cantor Rights to Purchase Exchangeable Units [Member] | Class A Common Stock [Member]
Related Party Transactions [Abstract]
Aggregate consideration amount | $																							$ 38,700,000
Previously-owned common stock purchased																							1,857,743
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
Relief Fund [Member]
Related Party Transactions [Abstract]
Interest-free loan to related party | $																																		$ 1,000,000
Promissory note from related party | $																																					$ 1,000,000
Promissory note repayment date																																	Aug. 04, 2016
Relief Fund [Member] | Accounts Payable, Accrued and Other Liabilities [Member]
Related Party Transactions [Abstract]
Charitable contributions | $	$ 30,700,000																												30,700,000				$ 30,700,000
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]
Repurchase of Class A common stock			166,238											970,639
Average price per share of common stock repurchased | $ / shares			$ 9.74											$ 8.72
Cantor and ELX [Member]
Related Party Transactions [Abstract]
Recognized related party revenues | $																																	24,200,000	25,300,000	28,400,000
Service charges | $																																	52,100,000	43,700,000	34,300,000
Compensation to leased employees | $																																	28,200,000	25,600,000	22,200,000
Cantor's share of net profit in Tower Bridge | $																																	$ 2,500,000	2,000,000	2,500,000
Cantor and CFGM [Member] | Class A Common Stock [Member]
Related Party Transactions [Abstract]
Convertible Notes, shares	14,683,401																			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
Cantor and Freedom International Brokerage [Member]
Related Party Transactions [Abstract]
Receivables from Freedom International Brokerage | $	$ 1,300,000																												1,300,000				$ 1,300,000	4,100,000
Receivables from Cantor related to open derivative contracts | $	3,000,000																												3,000,000				3,000,000	900,000
Payables to Cantor related to open derivative contracts | $	1,000,000																												1,000,000				1,000,000	400,000
Payables to Cantor related to pending equity trades | $	0																												0				0	4,600,000
Employee Loans [Member]
Related Party Transactions [Abstract]
Employee loans | $	$ 267,500,000																												$ 267,500,000				267,500,000	158,200,000
Compensation expense related to employee loans | $																																	55,800,000	86,700,000	25,700,000
Interest income | $																																	5,800,000	3,900,000	3,600,000
CastleOak [Member]
Related Party Transactions [Abstract]
Advisory fees payable | $																																		7,100,000
CastleOak [Member] | Underwriting Fees [Member]
Related Party Transactions [Abstract]
Underwriting fees | $																																			18,000
CCRE [Member]
Related Party Transactions [Abstract]
Recognized related party revenues | $																																	8,900,000	2,000,000	1,200,000
Payments of referrals for leasing or other services | $																																	$ 400,000	$ 300,000	$ 0