Compensation - Narrative (Details) $ / shares in Units, $ in Thousands		12 Months Ended
	Oct. 18, 2024 shares	Dec. 31, 2025 USD ($) $ / shares shares	Dec. 31, 2024 USD ($) shares	Dec. 31, 2023 USD ($) shares	Feb. 18, 2025	Oct. 23, 2024	Oct. 17, 2024 shares	Sep. 23, 2024	Dec. 13, 2017 shares
Share-based Compensation Arrangement by Share-based Payment Award
Limited partnership units exchange ratio		0.4545			0.9279	0.9257		0.9248
Compensation expense (benefit) | $		$ 0	$ (700)	$ 0
Common stock, conversion for each restricted stock unit settled (in shares)		1
Non Distribution Earning Units
Share-based Compensation Arrangement by Share-based Payment Award
Unit granted during period (in shares)		10,600,000	12,300,000	24,300,000
Number of shares vested and converted (in shares)		7,900,000	10,400,000	11,600,000
Newmark Holdings, L.P.
Share-based Compensation Arrangement by Share-based Payment Award
Limited partnership units exchange ratio		0.4545
Newmark Holdings Units
Share-based Compensation Arrangement by Share-based Payment Award
Compensation expense (benefit) | $		$ 251,188	$ 163,744	$ 124,805
Newmark Holdings Units | Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award
Unrecognized compensation expense | $		$ 59,700
Cost not yet recognized, period for recognition		4 years
Compensation expense (benefit) | $		$ 7,900
Earnings per share, decrease, basic (in dollars per share) | $ / shares		$ 0.02
Earnings per share, decrease, diluted (in dollars per share) | $ / shares		$ 0.02
Newmark Holdings Units | Limited Partnership Units
Share-based Compensation Arrangement by Share-based Payment Award
Award vesting period		7 years
Shares purchased for award (in shares)		4,600,000
Fair value of non-vested | $		$ 22,300
Unrecognized compensation expense | $		$ 10,100
Cost not yet recognized, period for recognition		2 years 1 month 6 days
Newmark Holdings Units | Non Distribution Earning Units | Limited Partnership Units
Share-based Compensation Arrangement by Share-based Payment Award
Shares purchased for award (in shares)		3,000,000.0
Maximum | Newmark Holdings, L.P. | Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award
Award vesting period		8 years
Maximum | Newmark Holdings Units | Limited Partnership Units
Share-based Compensation Arrangement by Share-based Payment Award
Award vesting period		7 years
Class A Common Stock
Share-based Compensation Arrangement by Share-based Payment Award
Limited partnership units exchange ratio									1
Class A Common Stock | Newmark Holdings Units
Share-based Compensation Arrangement by Share-based Payment Award
Limited partnership units exchange ratio		0.9264
Newmark Equity Plan | Class A Common Stock
Share-based Compensation Arrangement by Share-based Payment Award
Shares authorized to be delivered pursuant to awards granted (in shares)							500,000,000.0		400,000,000.0
Additional share authorized (in shares)	100,000,000.0
Shares registered to be delivered pursuant to awards granted (in shares)		500,000,000.0
Shares purchased for award (in shares)		126,100,000
Shares available for future awards (in shares)		373,900,000