Related Party Transactions - Transfer of Employees to Newmark and Other Related Party Transactions (Details) shares in Millions		1 Months Ended			12 Months Ended
	May 01, 2018 USD ($) Employee	Jul. 31, 2020 USD ($)	Feb. 28, 2019 USD ($)	Oct. 31, 2018 USD ($)	Dec. 31, 2020 USD ($) shares	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Related Party Transaction
Proceeds from issuance of EPUs					$ 0	$ 0	$ 262,169,000
Total stockholders’ equity					655,049,000	599,664,000
Redeemable partnership interests					20,045,000	21,517,000	26,170,000
Payments to related party					0	0	$ 858,428,000
Payables to related parties					4,392,000	38,090,000
CCRE
Related Party Transaction
Number of employees transferred | Employee	5
Proceeds from limited partnership units				$ 6,900,000
Total stockholders’ equity					6,900,000
Redeemable partnership interests					$ 2,200,000
Maximum revenue share to related party in first two years	$ 3,300,000
Payments to related party		$ 3,300,000
Payables to related parties						$ 2,600,000
CCRE | Newmark Holdings, L.P.
Related Party Transaction
Proceeds from issuance of EPUs				6,700,000
Limited partnership unit cash distributions				$ 200,000
Issuance of additional limited partners units in exchange (in shares) | shares					2.2
Issuance of additional limited partners units in exchange for cash payment					$ 500,000
Issuance of additional limited partnership units with capital account					$ 2,200,000
Cantor Fitzgerald Limited Partnership And B G C Partners Incorporation | Government Sponsored Enterprise Loans
Related Party Transaction
Maximum amount per loan			$ 100,000,000.0
Limit on loans that have not yet been acquired or sold			250,000,000.0
Limit on loans outstanding			$ 250,000,000.0