Related Party Transactions - Additional Information (Detail)																					1 Months Ended	3 Months Ended		7 Months Ended	9 Months Ended		12 Months Ended
	May 17, 2022 USD ($) shares	Mar. 14, 2022 USD ($) $ / shares shares	Dec. 21, 2021 USD ($) shares	Oct. 28, 2021 USD ($) shares	Jul. 30, 2021 USD ($)	Jun. 28, 2021 USD ($) $ / shares shares	Jun. 24, 2021	Apr. 29, 2021 USD ($) shares	Apr. 23, 2021 USD ($) $ / shares shares	Mar. 31, 2021 USD ($) shares	Feb. 22, 2021 USD ($) shares	Jul. 10, 2020 USD ($)	Mar. 20, 2020	Sep. 27, 2019 USD ($)	Nov. 23, 2018 USD ($) shares	Aug. 06, 2018 USD ($)	Jul. 24, 2018 USD ($)	Oct. 25, 2016 shares	May 27, 2016 USD ($)	Jun. 05, 2015 shares	May 31, 2020 USD ($) ft²	Sep. 30, 2022 USD ($) shares	Sep. 30, 2021 USD ($) shares	Jul. 31, 2021 USD ($)	Sep. 30, 2022 USD ($) shares	Sep. 30, 2021 USD ($) shares	Dec. 31, 2015 USD ($)	Jun. 05, 2022	Dec. 31, 2021 USD ($)	May 31, 2021 USD ($)	Apr. 08, 2021 shares	Feb. 25, 2021 USD ($)	Aug. 14, 2020 USD ($)	Aug. 05, 2020 USD ($)	Jun. 11, 2020 USD ($)	Mar. 02, 2020 $ / shares	Feb. 25, 2020 USD ($)	Mar. 19, 2018 USD ($)	Nov. 04, 2016	Aug. 31, 2013 USD ($)
Related Party Transactions [Abstract]
Repurchase agreements																						$ 1,013,000			$ 1,013,000				$ 0
Commissions																						299,430,000	$ 367,016,000		965,636,000	$ 1,192,004,000
Common stock, exchange ratio															1													1
Payables to Cantor related to open derivative contracts																						78,362,000			78,362,000				53,764,000
Employee loans																						313,827,000			313,827,000				286,967,000
Number of H units redeemed (in shares) | shares						1,131,774
Payment related to H units redeemed						$ 7,017,000
Number of preferred H units redeemed (in shares) | shares						1,018,390
Payment related tax for redeemed preferred H units						$ 7,983,000
Due to related parties																						0			0				8,300,000
Equity investment																									588,000	870,000
Receivables from related parties																						6,276,000			6,276,000				5,237,000
Revenues																						416,567,000	473,747,000		1,358,787,000	1,553,773,000
Futures Exchange Group
Related Party Transactions [Abstract]
Payments to acquire businesses					$ 4,900,000
Aqua
Related Party Transactions [Abstract]
Increase in authorization amount for loans and investments, other credit support arrangements																																$ 1,000,000					$ 1,000,000
Authorization amount for loans and investments, other credit support arrangements																																$ 21,200,000
Equity investment																						100,000	$ 200,000		600,000	$ 900,000
Receivables from related parties																						$ 980,000			$ 980,000
Loan receivable, basis spread																						6.00%			6.00%
Stephen M. Merkel
Related Party Transactions [Abstract]
Number of non-exchangeable units redeemed (in shares) | shares								108,350
Number of non-exchangeable PSUs (in shares) | shares								273,612
Payment related to non-exchangeable PSUs redeemed upon exchange								$ 0
Number of non-exchangeable PPSUs redeemed | shares								101,358
Number of non-exchangeable PPSUs (in shares) | shares								250,659
Payments related to non-exchangeable PPSUs redeemed upon exchange								$ 575,687
Number of PSU approved redemption (in shares) | shares			90,366
Payment related to PSU redeemed			$ 0
Number of PPSU approved redemption (in shares) | shares			149,301
Payment related to non exchangeable PPSU redeemed			$ 555,990
Mr. Lutnick
Related Party Transactions [Abstract]
Number of non-exchangeable PSUs (in shares) | shares			2,011,731
Payment related to non-exchangeable PSUs redeemed upon exchange			$ 0
Payments related to non-exchangeable PPSUs redeemed upon exchange			$ 1,525,706
Number of H units redeemed (in shares) | shares			376,651
Payment related to H units redeemed			$ 2,339,003
Number of preferred H units redeemed (in shares) | shares			463,969
Number of non exchangeable P P S U approved redemption (in shares) | shares			1,939,896
Payment related to non exchangeable PPSU approved redemption			$ 10,851,803
Number of exchangeable PPSU (in shares) | shares			425,766
Number of HDUs redeemed (in shares) | shares			376,651
Payment related for redeemed preferred H units (in shares)			$ 2,661,000
Mr. Lutnick | Exchange LPUs for common stock
Related Party Transactions [Abstract]
Number of non-exchangeable LPU (in shares) | shares						88,636
Number of exchangeable LPU exchanged for issuance of shares (in shares) | shares						520,380
Exchange share price (in dollars per share) | $ / shares						$ 5.86
Number of shares redeemed (in shares) | shares						0
Mr. Lutnick | Exchange PLPUs for common stock
Related Party Transactions [Abstract]
Number of exchangeable PLPUs (in shares) | shares						425,765
Payment related tax for redeemed PLPU						$ 1,525,705
Sean A. Windeatt
Related Party Transactions [Abstract]
Number of exchange rights grant (in shares) | shares											123,713
Number of non-exchangeable LPU (in shares) | shares											123,713
Number of PLPU share issued for non-exchangeable (in shares) | shares											28,477
Payment of withholding tax rate for common stock issue											$ 178,266
Shares authorized to be repurchased (in shares) | shares		135,514							123,713
Exchange share price (in dollars per share) | $ / shares		$ 4.08							$ 5.65																											$ 5.38
Number of shares redeemed (in shares) | shares		27,826							28,477
Number of shares redeemed, value		$ 134,678							$ 178,266
Remaining number of shares authorized to be repurchased (in shares) | shares																															62,211
Number of non-exchangeable LPU-NEWs | shares		135,514
Number of non-exchangeable PLPU | shares		27,826
Average determination price | $ / shares		$ 4.84
Debt securities
Related Party Transactions [Abstract]
Debt instrument, authorized repurchase amount																																			$ 50,000,000
Debt instrument, remaining authorized purchase amount																						$ 50,000,000			$ 50,000,000
5.125% senior notes due 2021
Related Party Transactions [Abstract]
Principal amount of debt component																			$ 300,000,000
Stated interest rate																			5.125%
5.375% senior notes due 2023
Related Party Transactions [Abstract]
Principal amount of debt component																	$ 450,000,000
Stated interest rate																	5.375%
3.750% senior notes due october 1, 2024
Related Party Transactions [Abstract]
Principal amount of debt component														$ 300,000,000
Stated interest rate														3.75%
4.375% senior notes
Related Party Transactions [Abstract]
Principal amount of debt component												$ 300,000,000
Stated interest rate												4.375%										4.375%			4.375%
5.125% senior notes
Related Party Transactions [Abstract]
Principal amount of debt component																			$ 300,000,000															$ 300,000,000
Stated interest rate																			5.125%			5.125%			5.125%
Class B Common Stock
Related Party Transactions [Abstract]
Issuance of class A common stock (net of costs) (in shares) | shares																						0	0		0	0
Class A Common Stock
Related Party Transactions [Abstract]
Issuance of class A common stock (net of costs) (in shares) | shares																						101,786	100,128		445,245	366,043
Stock repurchased during period (in shares) | shares																						12,400,000	24,400,000		21,100,000	41,900,000
Class A Common Stock | Stephen M. Merkel
Related Party Transactions [Abstract]
Issuance of class A common stock (net of costs) (in shares) | shares			90,366					108,350
Stock repurchased during period (in shares) | shares								108,350
Class A Common Stock | Mr. Lutnick
Related Party Transactions [Abstract]
Issuance of class A common stock (net of costs) (in shares) | shares			2,011,731
Class A Common Stock | Mr. Lutnick | Exchange LPUs for common stock
Related Party Transactions [Abstract]
Issuance of class A common stock (net of costs) (in shares) | shares						520,380
Common stock, shares issued net of shares for tax withholdings (in shares) | shares						365,229
Class A Common Stock | Mr. Lutnick | Exchange PLPUs for common stock
Related Party Transactions [Abstract]
Issuance of class A common stock (net of costs) (in shares) | shares						88,636
Common stock, shares issued net of shares for tax withholdings (in shares) | shares						41,464
Class A Common Stock | Sean A. Windeatt
Related Party Transactions [Abstract]
Number of exchangeable LPU exchanged for issuance of shares (in shares) | shares											123,713
Class B Units | Lucera
Related Party Transactions [Abstract]
Purchase of units (in shares) | shares																		9,000
Percentage of outstanding common stock owned by parent																																							100.00%
Cantor
Related Party Transactions [Abstract]
Repurchase agreements																						$ 1,000,000			$ 1,000,000				0
Futures Exchange Group | Cantor
Related Party Transactions [Abstract]
Related party transaction, contributed capital																						$ 0		$ 5,300,000	$ 0
Tower Bridge International Services LP | BGC Partners, Inc.
Related Party Transactions [Abstract]
Company ownership of tower bridge																									52.00%
Tower Bridge International Services LP | Cantor
Related Party Transactions [Abstract]
Ownership percentage by noncontrolling owners																						48.00%			48.00%
Aqua | BGC Partners, Inc. | Aqua
Related Party Transactions [Abstract]
Percentage of ownership interest																						49.00%			49.00%
Aqua | Cantor
Related Party Transactions [Abstract]
Investment ownership percentage																						51.00%			51.00%
Cantor
Related Party Transactions [Abstract]
Mark-up cost of services																									7.50%
Cantor's share of net profit (loss) in tower bridge																						$ 200,000	$ 700,000		$ 6,000	$ 1,300,000
Related party revenues																						3,900,000	3,500,000		10,800,000	11,500,000
Service charges																						20,300,000	18,700,000		61,800,000	60,000,000
Compensation to leased employees																						13,700,000	13,000,000		43,500,000	44,400,000
Recognition of share of FX gains																						1,600,000	200,000		3,600,000	200,000
Commissions																						100,000	24,000		300,000	100,000
Investment authorization in asset-backed commercial paper program																																								$ 350,000,000
Investment in asset-backed commercial paper program																						0			0				0
Common stock, issued during the period, additional consideration															$ 0
Reverse purchase agreement outstanding																						0			0				0
Cantor | Futures Exchange Group
Related Party Transactions [Abstract]
Business combination, indemnified expenses (up to)					$ 1,000,000
Indemnification assets																						1,000,000			1,000,000				400,000
Cantor | Lucera
Related Party Transactions [Abstract]
Related party revenues																						0	100,000		0	300,000
Cantor | Revolving credit facility
Related Party Transactions [Abstract]
Principal amount of debt component																$ 400,000,000																						$ 250,000,000
Debt instrument, extended term																1 year
Debt instrument, non-extension notice term																6 months
Debt instrument, basis spread on variable rate													1.00%
Line of credit facility, outstanding amount																						0			0				0
Interest expense from affiliate																						$ 0	0		$ 0	0
CF Group Management, Inc.
Related Party Transactions [Abstract]
Right to exchange from class a to class b common stock (up to) (in shares) | shares															700,000					34,600,000
Common stock, issued during the period, additional consideration															$ 0
Cantor rights to purchase exchangeable units
Related Party Transactions [Abstract]
Right to exchange from class a to class b common stock (up to) (in shares) | shares															10,300,000										23,600,000
Limited partnership units, exchange ratio																									1
Cantor rights to purchase exchangeable units | Maximum
Related Party Transactions [Abstract]
Right to exchange from class a to class b common stock (up to) (in shares) | shares																				34,600,000					23,600,000
Cantor rights to purchase exchangeable units | BGC Holdings LPUs
Related Party Transactions [Abstract]
Aggregate cantor units as result of redemption | shares	427,494			460,929						1,149,684
Aggregate consideration of cantor units as result of redemption	$ 841,010			$ 715,605						$ 2,104,433
Number of founding partner interests as result of redemption (in shares) | shares	427,494			460,929						1,149,684
Aggregate cantor units (in shares) | shares	52,681			1,179,942						1,618,376
Aggregate consideration of cantor units	$ 105,867			$ 2,033,838						$ 3,040,411
Number of founding partner interests exchanged (in shares) | shares	52,681			1,179,942						1,618,376
Founding partner units remaining (in shares) | shares																						400,000			400,000
Cantor and CFGM | Class B Common Stock
Related Party Transactions [Abstract]
Right to exchange from class a to class b common stock (up to) (in shares) | shares																									23,600,000
Cantor and Freedom
Related Party Transactions [Abstract]
Receivables from freedom																						$ 1,600,000			$ 1,600,000				1,400,000
Receivables from cantor related to open derivative contracts																						10,100,000			10,100,000				2,500,000
Payables to Cantor related to open derivative contracts																						8,100,000			8,100,000				1,500,000
Payables to cantor related to pending equity trades																						504,800,000			504,800,000				0
Employee loans
Related Party Transactions [Abstract]
Employee loans																						313,800,000			313,800,000				287,000,000
Compensation expense related to employee loans																						10,700,000	11,100,000		35,100,000	45,700,000
Interest income																						1,700,000	$ 2,000,000		5,200,000	$ 7,500,000
CF & Co
Related Party Transactions [Abstract]
Repurchase agreements																						$ 1,000,000			$ 1,000,000				0
Issuance of class A common stock (net of costs) (in shares) | shares																						0	0		0	0
Related party expenses																						$ 0	$ 0		$ 0	$ 0
Securities loaned																						0			0				0
Guarantee fees																						31,000	31,000		100,000	100,000
CF & Co | 5.125% senior notes due 2021 | Underwriting fees
Related Party Transactions [Abstract]
Related party expenses																			$ 500,000
Purchased senior notes																																	$ 15,000,000
CF & Co | 5.375% senior notes due 2023
Related Party Transactions [Abstract]
Advisory fees																	$ 200,000
CF & Co | 5.375% senior notes due 2023 | Underwriting fees
Related Party Transactions [Abstract]
Related party expenses																	$ 300,000
CF & Co | 4.375% senior notes
Related Party Transactions [Abstract]
Purchased senior notes																						14,500,000			14,500,000
CF & Co | 4.375% senior notes | Underwriting fees
Related Party Transactions [Abstract]
Related party expenses												$ 200,000
Castle Oak | 3.750% senior notes due october 1, 2024 | Underwriting fees
Related Party Transactions [Abstract]
Related party expenses														$ 200,000
Cantor Fitzgerald Relief Fund
Related Party Transactions [Abstract]
Remaining liability associated with charitable contributions																						0			0				1,700,000
Cantor Fitzgerald Relief Fund | Other expenses
Related Party Transactions [Abstract]
Charitable contributions																											$ 40,000,000
Additional Cantor Fitzgerald Relief Fund
Related Party Transactions [Abstract]
Remaining expense related to charitable contributions																						6,400,000	7,200,000		6,400,000	7,200,000
Additional Cantor Fitzgerald Relief Fund | Accounts payable and accrued liabilities
Related Party Transactions [Abstract]
Remaining liability associated with charitable contributions																						12,200,000			12,200,000				$ 8,300,000
RKF Retail Holdings LLC
Related Party Transactions [Abstract]
Lessee operating lease sublease term																					1 year
Area of sublease | ft²																					21,000
BGC U.S OpCo
Related Party Transactions [Abstract]
Operating lease cost																					$ 1,100,000
Rent payment under lease term																							100,000			500,000
Aurel BGC SAS | Cantor
Related Party Transactions [Abstract]
Revenues																						0	0		0	0
Fees payable																						$ 0	$ 0		$ 0	$ 0
Aurel BGC SAS | Cantor
Related Party Transactions [Abstract]
Percentage of revenue shared between related parties							80.00%
Revenue sharing agreement, term							12 months
Poten & Partners
Related Party Transactions [Abstract]
Monthly rent expense																														$ 15,000