Related Party Transactions - Transactions with Executive Officers and Directors (Details)														1 Months Ended						3 Months Ended						9 Months Ended		12 Months Ended
	Sep. 21, 2023 $ / shares shares	Jul. 12, 2023 USD ($)	Jul. 12, 2023 GBP (£)	Jul. 11, 2023 GBP (£)	Jul. 10, 2023 USD ($) $ / shares shares	Jul. 02, 2023 shares	Jul. 01, 2023 USD ($) shares	Jun. 30, 2023 USD ($)	Jun. 02, 2023 $ / shares shares	May 18, 2023 USD ($) $ / shares shares	Apr. 18, 2023 $ / shares shares	Aug. 11, 2022 USD ($) $ / shares shares	Apr. 01, 2021 shares	Sep. 30, 2023 shares	Aug. 31, 2023 shares	Jul. 31, 2023 shares	Sep. 30, 2022 shares	Aug. 31, 2022 shares	Jul. 31, 2022 shares	Sep. 30, 2023 $ / shares shares	Jun. 30, 2023 shares	Mar. 31, 2023 shares	Sep. 30, 2022 $ / shares shares	Jun. 30, 2022 shares	Mar. 31, 2022 shares	Sep. 30, 2023 USD ($) $ / shares shares	Sep. 30, 2022 $ / shares shares	Dec. 31, 2022 shares	Jun. 08, 2023 $ / shares shares	Mar. 14, 2022 $ / shares shares
Related Party Transaction [Line Items]
Deed of amendment, notice period		24 months	24 months
Repurchase of class A common stock (in shares)														3,474,000	1,612,000	3,000,000	3,448,000	5,916,000	3,033,000	8,087,000	9,814,000	846,000	12,397,000	8,745,000	0	18,747,000	21,142,000
Class A Common Stock
Related Party Transaction [Line Items]
Share price (in dollars per share) | $ / shares					$ 4.45
Repurchase of class A common stock (in shares)																				8,086,750			12,396,735			18,746,467	21,142,045
Issuance of common stock (in shares)																				55,348						234,931
Equity-based compensation (in shares)																				6,490,733			448,014			9,120,746	3,018,337
Stock repurchased, weighted average price (in dollars per share) | $ / shares																				$ 4.99			$ 4.03			$ 4.70	$ 3.75
Shares granted in period (in shares)							600,000,000
Class B Common Stock
Related Party Transaction [Line Items]
Issuance of common stock (in shares)						15,800,000	64,000,000													64,000,000						64,000,000		0
Restricted Stock Units (RSUs)
Related Party Transaction [Line Items]
Share-based payment arrangement, decrease for tax withholding obligation | $							$ 74,000,000	$ 49,200,000
Aggregate estimated grant date fair value | $		$ 3,986,600																								$ 43,011,000
Shares granted in period (in shares)							25,300,000
Restricted Stock Units (RSUs) | Mr. Windeatt
Related Party Transaction [Line Items]
Share-based payment arrangement, decrease for tax withholding obligation | $					$ 780,333
Vested in period (in shares)					720,509
Related Party
Related Party Transaction [Line Items]
Issuance of common stock (in shares)																				0			0			0	0
Shares withheld for tax withholding obligation, price per share (in dollars per share) | $ / shares										$ 4.61
Related Party | Mr. Merkel
Related Party Transaction [Line Items]
Shares withheld for tax withholding obligation, price per share (in dollars per share) | $ / shares										$ 4.61
Related Party | Mr. Lutnick
Related Party Transaction [Line Items]
Determination amount | $										$ 6,650,000
Related Party | Mr. Windeatt
Related Party Transaction [Line Items]
Drawings, aggregate amount, per year | £			£ 700,000	£ 600,000
Number of non-exchangeable LPU-NEWs (in shares)																														135,514
Number of non-exchangeable PLPU (in shares)																														27,826
Average determination price (in dollars per share) | $ / shares																														$ 4.84
Exchange share price (in dollars per share) | $ / shares												$ 4.08
Shares authorized to be repurchased (in shares)												135,514
Number of shares redeemed (in shares)												27,826
Number of shares redeemed, value | $												$ 134,678
Related Party | Class A Common Stock | Mr. Merkel
Related Party Transaction [Line Items]
Repurchase of class A common stock (in shares)									150,000
Stock repurchased, weighted average price (in dollars per share) | $ / shares									$ 4.21
Grants in period, net (in shares)										196,525
Related Party | Class A Common Stock | Mr. Lutnick
Related Party Transaction [Line Items]
Grants in period, net (in shares)										5,710,534
Related Party | Class A Common Stock | Reporting Person
Related Party Transaction [Line Items]
Share price (in dollars per share) | $ / shares	$ 5.29
Repurchase of class A common stock (in shares)	474,808
Related Party | Class A Common Stock | Ms. Bell
Related Party Transaction [Line Items]
Repurchase of class A common stock (in shares)											21,786
Stock repurchased, weighted average price (in dollars per share) | $ / shares											$ 4.59
Related Party | NPU-CV, PSU-CV & PSU | Mr. Merkel
Related Party Transaction [Line Items]
Shares redeemed in period | $										$ 0
Related Party | NPSU-CV | Mr. Merkel
Related Party Transaction [Line Items]
Shares redeemed in period (in shares)										148,146
Related Party | PSU-CV | Mr. Merkel
Related Party Transaction [Line Items]
Shares redeemed in period (in shares)										33,585
Related Party | PSU | Mr. Merkel
Related Party Transaction [Line Items]
Shares redeemed in period (in shares)										74,896
Related Party | PSU | Mr. Lutnick
Related Party Transaction [Line Items]
Shares redeemed in period | $										$ 0
Related Party | NPPSU-CV & PPSU-CV | Mr. Merkel
Related Party Transaction [Line Items]
Shares redeemed in period | $										$ 843,750
Related Party | NPPSU-CV | Mr. Merkel
Related Party Transaction [Line Items]
Shares redeemed in period (in shares)										148,146
Determination amount | $										$ 681,250
Related Party | PPSU-CV | Mr. Merkel
Related Party Transaction [Line Items]
Shares redeemed in period (in shares)										33,585
Determination amount | $										$ 162,500
Related Party | Share-Based Payment Arrangement | Class A Common Stock
Related Party Transaction [Line Items]
Shares granted in period (in shares)																				1,000,000
Related Party | Share-Based Payment Arrangement | Class A Common Stock | Mr. Merkel
Related Party Transaction [Line Items]
Shares granted in period (in shares)										256,627
Related Party | Share-Based Payment Arrangement | Class A Common Stock | Mr. Lutnick
Related Party Transaction [Line Items]
Grants in period, net (in shares)										232,610
Related Party | Share-Based Payment Arrangement | Class A Common Stock | Mr. Lutnick | Exchangeable PSU
Related Party Transaction [Line Items]
Shares granted in period (in shares)										520,380
Related Party | Share-Based Payment Arrangement | Class A Common Stock | Mr. Lutnick | Non-exchangeable PSU
Related Party Transaction [Line Items]
Shares granted in period (in shares)										11,332,727
Related Party | Non-exchangeable PSUs & PPSUs | Prior To 5/18/2023 | Mr. Lutnick
Related Party Transaction [Line Items]
Determination amount | $										$ 474,195
Related Party | Non-exchangeable PSU | Mr. Lutnick
Related Party Transaction [Line Items]
Shares redeemed in period (in shares)										11,332,727
Related Party | Non-exchangeable PSU | Prior To 5/18/2023 | Mr. Lutnick
Related Party Transaction [Line Items]
Shares redeemed in period (in shares)										7,879,736
Related Party | Non-exchangeable PPSU | Prior To 5/18/2023 | Mr. Lutnick
Related Party Transaction [Line Items]
Shares redeemed in period (in shares)										103,763
Related Party | Incrementally Monetized Non-exchangeable PSUs & PPSUs | Mr. Lutnick
Related Party Transaction [Line Items]
Shares redeemed in period | $										$ 6,650,000
Related Party | Incrementally Monetized Non-exchangeable PSUs & PPSUs | On 5/18/2023 | Mr. Lutnick
Related Party Transaction [Line Items]
Determination amount | $										$ 6,175,805
Related Party | Incrementally Monetized Non-exchangeable PSU | On 5/18/2023 | Mr. Lutnick
Related Party Transaction [Line Items]
Shares redeemed in period (in shares)										3,452,991
Related Party | Incrementally Monetized Non-exchangeable PPSU | Mr. Lutnick
Related Party Transaction [Line Items]
Shares redeemed in period (in shares)										1,451,805
Related Party | Incrementally Monetized Non-exchangeable PPSU | On 5/18/2023 | Mr. Lutnick
Related Party Transaction [Line Items]
Shares redeemed in period (in shares)										1,348,042
Related Party | Exchangeable PSU | Mr. Lutnick
Related Party Transaction [Line Items]
Shares redeemed in period (in shares)										520,380
Related Party | Non-exchangeable HDU | Mr. Lutnick
Related Party Transaction [Line Items]
Shares redeemed in period (in shares)										1,474,930
Related Party | Non-exchangeable HDU | Mr. Lutnick | BGC Parnters
Related Party Transaction [Line Items]
Shares redeemed in period | $										$ 2,100,000
Related Party | Non-exchangeable HDU | Mr. Lutnick | Newmark
Related Party Transaction [Line Items]
Shares redeemed in period | $										$ 9,148,000
Related Party | Non-exchangeable Limited Partnership Interests | Reporting Person
Related Party Transaction [Line Items]
Shares granted in period (in shares)													128,279
Shares repurchased (in shares)																													128,279
Shares repurchased (in dollars per share) | $ / shares																													$ 4.79
Related Party | Restricted Stock Units (RSUs)
Related Party Transaction [Line Items]
Shares granted in period (in shares)																				16,900,000