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Amount of amortization expense attributable to debt issuance costs.

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Percentage points added to the reference rate to compute the variable rate on the debt instrument.

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Face (par) amount of debt instrument at time of issuance.

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Contractual interest rate for funds borrowed, under the debt agreement.

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Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

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Amount after unamortized (discount) premium and debt issuance costs of long-term debt classified as noncurrent and excluding amounts to be repaid within one year or the normal operating cycle, if longer. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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Schedule I - Parent Company Only - Long-Term Debt (Detail) - USD ($)								12 Months Ended
	Feb. 26, 2020	Nov. 28, 2018	Nov. 06, 2018	Sep. 26, 2018	Jun. 19, 2018	Dec. 13, 2017	Sep. 08, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Nov. 22, 2017
Debt Instrument [Line Items]
Long-term debt								$ 589,294,000	$ 537,926,000
Repayments of credit agreement								9,545,964,000	8,000,725,000	$ 8,742,295,000
Senior Notes \| 6.125% Senior Notes
Debt Instrument [Line Items]
Debt instrument face amount			$ 550,000,000.0
Stated interest rate			6.125%
Issued price percentage			98.937%
Yield percentage			6.375%
Long-term debt								540,377,000	537,926,000
Debt issuance costs								5,000,000.0	6,600,000
Debt discount								4,700,000	5,800,000
Amortization of debt issuance discounts								1,000,000.0	200,000
Amortization of debt issuance costs								1,300,000	200,000
Interest expense								34,700,000	5,500,000
Converted Term Loan
Debt Instrument [Line Items]
Long-term debt								$ 0
Interest expense									12,900,000	700,000
Repayments of convertible debt			$ 134,000,000.0	$ 113,200,000	$ 152,900,000
Converted Term Loan \| LIBOR or Defined Base Rate \| Minimum
Debt Instrument [Line Items]
Basis spread on variable rate							0.50%
Converted Term Loan \| LIBOR or Defined Base Rate \| Maximum
Debt Instrument [Line Items]
Basis spread on variable rate							3.25%
Term Loan
Debt Instrument [Line Items]
Interest expense									2,600,000	700,000
Maximum revolving credit							$ 575,000,000.0
Repayments of credit agreement						$ 304,300,000			270,700,000
Term Loan \| LIBOR or Defined Base Rate \| Minimum
Debt Instrument [Line Items]
Basis spread on variable rate							0.50%
Term Loan \| LIBOR or Defined Base Rate \| Maximum
Debt Instrument [Line Items]
Basis spread on variable rate							3.25%
Revolving Credit Facility
Debt Instrument [Line Items]
Maximum revolving credit											$ 400,000,000.0
Revolving Credit Facility \| Line of Credit
Debt Instrument [Line Items]
Long-term debt term		3 years
Stated interest rate								3.76%
Long-term debt								$ 48,917,000	0
Debt issuance costs								1,100,000
Amortization of debt issuance costs								600,000
Interest expense								2,500,000
Maximum revolving credit		$ 250,000,000.0
Revolving Credit Facility \| Line of Credit \| Subsequent Event
Debt Instrument [Line Items]
Maximum revolving credit	$ 425,000,000.0
Revolving Credit Facility \| Line of Credit \| LIBOR \| Subsequent Event
Debt Instrument [Line Items]
Basis spread on variable rate	1.75%
Revolving Credit Facility \| Line of Credit \| Interest Rate Option Two \| Federal Funds Rate
Debt Instrument [Line Items]
Basis spread on variable rate		0.50%
Revolving Credit Facility \| Line of Credit \| Interest Rate Option Two \| LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate		0.10%
Revolving Credit Facility \| Line of Credit \| Interest Rate Option One \| LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate		2.00%
Revolving Credit Facility \| Line of Credit \| Interest Rate Option One \| LIBOR \| Minimum
Debt Instrument [Line Items]
Basis spread on variable rate		0.25%
Revolving Credit Facility \| Line of Credit \| Interest Rate Option One \| LIBOR \| Maximum
Debt Instrument [Line Items]
Basis spread on variable rate		1.25%
NEWMARK Group Inc Parent
Debt Instrument [Line Items]
Long-term debt								589,294,000	537,926,000
NEWMARK Group Inc Parent \| Senior Notes \| 6.125% Senior Notes
Debt Instrument [Line Items]
Debt instrument face amount			$ 550,000,000.0
Stated interest rate			6.125%
Issued price percentage			98.937%
Yield percentage			6.375%
Long-term debt								540,400,000	537,900,000
Debt issuance costs								5,000,000.0	6,600,000
Debt discount								4,700,000	5,800,000
Amortization of debt issuance discounts								1,000,000.0	200,000
Amortization of debt issuance costs								1,300,000	200,000
Interest expense								34,700,000	5,500,000
NEWMARK Group Inc Parent \| Converted Term Loan
Debt Instrument [Line Items]
Long-term debt								$ 0	400,000,000.0
Interest expense									12,900,000	700,000
Repayments of convertible debt			$ 134,000,000.0	$ 113,200,000	$ 152,900,000
NEWMARK Group Inc Parent \| Converted Term Loan \| LIBOR or Defined Base Rate \| Minimum
Debt Instrument [Line Items]
Basis spread on variable rate								0.50%
NEWMARK Group Inc Parent \| Converted Term Loan \| LIBOR or Defined Base Rate \| Maximum
Debt Instrument [Line Items]
Basis spread on variable rate								3.25%
NEWMARK Group Inc Parent \| Term Loan
Debt Instrument [Line Items]
Interest expense									2,600,000	$ 700,000
Maximum revolving credit							$ 575,000,000.0
Repayments of credit agreement						$ 304,300,000			270,700,000
NEWMARK Group Inc Parent \| Term Loan \| LIBOR or Defined Base Rate \| Minimum
Debt Instrument [Line Items]
Basis spread on variable rate								0.50%
NEWMARK Group Inc Parent \| Term Loan \| LIBOR or Defined Base Rate \| Maximum
Debt Instrument [Line Items]
Basis spread on variable rate								3.25%
NEWMARK Group Inc Parent \| Revolving Credit Facility \| Line of Credit
Debt Instrument [Line Items]
Long-term debt term		3 years
Stated interest rate								3.76%
Long-term debt								$ 48,900,000	$ 0
Debt issuance costs								1,100,000
Amortization of debt issuance costs								600,000
Interest expense								$ 2,500,000
Maximum revolving credit		$ 250,000,000.0
NEWMARK Group Inc Parent \| Revolving Credit Facility \| Line of Credit \| Interest Rate Option Two \| Federal Funds Rate
Debt Instrument [Line Items]
Basis spread on variable rate		0.50%
NEWMARK Group Inc Parent \| Revolving Credit Facility \| Line of Credit \| Interest Rate Option Two \| LIBOR \| Minimum
Debt Instrument [Line Items]
Basis spread on variable rate		0.10%
NEWMARK Group Inc Parent \| Revolving Credit Facility \| Line of Credit \| Interest Rate Option One \| LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate		2.00%
NEWMARK Group Inc Parent \| Revolving Credit Facility \| Line of Credit \| Interest Rate Option One \| LIBOR \| Minimum
Debt Instrument [Line Items]
Basis spread on variable rate		0.25%
NEWMARK Group Inc Parent \| Revolving Credit Facility \| Line of Credit \| Interest Rate Option One \| LIBOR \| Maximum
Debt Instrument [Line Items]
Basis spread on variable rate		1.25%