Financial Guarantee Liability - Summary of Provisions for Risk Sharing (Detail) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2018	Mar. 31, 2017
Guarantees [Abstract]
Increase (decrease) to financial guarantee liability	$ 7	$ (5)
Decrease to credit enhancement asset	10	4
Total expense	$ 17	$ (1)

Increase decrease to financial guarantee liability.

No definition available.

Name:	nmrk_IncreaseDecreaseToFinancialGuaranteeLiability
Namespace Prefix:	nmrk_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration