Debt instrument basis spread on redemption discount rate.

No definition available.

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- Definition

Year when the debt instrument is scheduled to be fully repaid.

+ References

No definition available.

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- Definition

Debt instrument offering price percentage.

+ References

No definition available.

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- Definition

Proceeds from withdrew of cash pledge.

+ References

No definition available.

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- Definition

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

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- Definition

Description of the frequency of periodic payments (monthly, quarterly, annual).

+ References

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- Definition

Effective interest rate for the funds borrowed under the debt agreement considering interest compounding and original issue discount or premium.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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- Definition

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

+ References

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- Definition

Date when the debt instrument is scheduled to be fully repaid, in CCYY-MM-DD format.

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- Definition

Description of debt redemption features under terms of the debt agreement.

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- Definition

Start date of debt instrument redemption period, in CCYY-MM-DD format.

+ References

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- Definition

Date the declared dividend will be paid, in CCYY-MM-DD format.

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- Definition

The per share amount of a dividend declared, but not paid, as of the financial reporting date.

+ References

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- Definition

Date the dividend to be paid was declared, in CCYY-MM-DD format.

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- Definition

Date the holder must own the stock to be entitled to the dividend, in CCYY-MM-DD format.

+ References

No definition available.

+ Details

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- Definition

Amount of cash outflow for payment of an obligation from a lender, including but not limited to, letter of credit, standby letter of credit and revolving credit arrangements.

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- Definition

The cash outflow for debt initially having maturity due after one year or beyond the normal operating cycle, if longer.

+ References

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- Definition

The cash outflow for a borrowing having initial term of repayment within one year or the normal operating cycle, if longer.

+ References

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- Definition

Number of new stock issued during the period.

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- Definition

Detail information of subsequent event by type. User is expected to use existing line items from elsewhere in the taxonomy as the primary line items for this disclosure, which is further associated with dimension and member elements pertaining to a subsequent event.

+ References

No definition available.

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Subsequent Events - Additional Information (Detail) - USD ($)								3 Months Ended		9 Months Ended		12 Months Ended
	Dec. 05, 2018	Nov. 08, 2018	Nov. 06, 2018	Nov. 05, 2018	Oct. 24, 2018	Oct. 15, 2018	Oct. 04, 2018	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017	Dec. 09, 2014
5.375% Senior Notes Due 2019 [Member]
Subsequent Event [Line Items]
Stated interest rate								5.375%		5.375%		5.375%
Debt maturity year										2019
Principal amount of notes													$ 300,000,000
Debt instrument, periodic interest payment description										payable in cash on June 9 and December 9 of each year, commencing June 9, 2015.
Senior Notes maturity date										Dec. 09, 2019
5.375% Senior Notes Due 2019 [Member] \| Scenario Forecast [Member]
Subsequent Event [Line Items]
Repayments of outstanding borrowings	$ 300,000,000
6.125% Senior Notes Due 2023 [Member]
Subsequent Event [Line Items]
Stated interest rate								6.125%		6.125%
Class A Common Stock [Member]
Subsequent Event [Line Items]
Common stock, issued during the period										25,975,240		1,994,670
Class B Common Stock [Member]
Subsequent Event [Line Items]
Common stock, issued during the period								0	0	0	0
Subsequent Event [Member] \| Unsecured Debt [Member] \| Converted Term Loan [Member]
Subsequent Event [Line Items]
Repayments of outstanding borrowings			$ 134,000,000
Subsequent Event [Member] \| Senior Revolving Credit Agreement [Member] \| Unsecured Debt [Member]
Subsequent Event [Line Items]
Repayments of revolving credit						$ 125,000,000
Subsequent Event [Member] \| Cantor [Member]
Subsequent Event [Line Items]
Repayment of short-term debt							$ 80,000,000
Subsequent Event [Member] \| Class A Common Stock [Member]
Subsequent Event [Line Items]
Dividend declared per share					$ 0.18
Dividend payable declared date					Oct. 24, 2018
Dividend payable, date to be paid					Nov. 28, 2018
Dividend payable record date					Nov. 07, 2018
Subsequent Event [Member] \| Class A Common Stock [Member] \| Controlled Equity Offerings [Member]
Subsequent Event [Line Items]
Common stock, issued during the period		1,200,000
Subsequent Event [Member] \| Class B Common Stock [Member]
Subsequent Event [Line Items]
Dividend declared per share					$ 0.18
Dividend payable declared date					Oct. 24, 2018
Dividend payable, date to be paid					Nov. 28, 2018
Dividend payable record date					Nov. 07, 2018
Newmark [Member] \| 5.375% Senior Notes Due 2019 [Member] \| Scenario Forecast [Member]
Subsequent Event [Line Items]
Repayments of outstanding borrowings	300,000,000
Newmark [Member] \| Subsequent Event [Member] \| 6.125% Senior Notes Due 2023 [Member]
Subsequent Event [Line Items]
Stated interest rate			6.125%	6.125%
Debt maturity year			2023
Principal amount of notes			$ 550,000,000
Debt instrument offering price percentage			98.937%
Debt instrument, yield percentage			6.375%
Debt instrument, periodic interest payment description			The 6.125% Senior Notes bear an interest rate of 6.125% per annum, payable on each May 15 and November 15, beginning on May 15, 2019
Senior Notes maturity date			Nov. 15, 2023
Newmark [Member] \| Subsequent Event [Member] \| Unsecured Debt [Member] \| Converted Term Loan [Member]
Subsequent Event [Line Items]
Repayments of outstanding borrowings			$ 134,000,000
Newmark [Member] \| Subsequent Event [Member] \| Intercompany Credit Agreement [Member]
Subsequent Event [Line Items]
Repayments of outstanding borrowings			112,500,000				252,000,000
Newmark [Member] \| Subsequent Event [Member] \| Intercompany Credit Agreement [Member] \| 6.125% Senior Notes Due 2023 [Member]
Subsequent Event [Line Items]
Repayments of outstanding borrowings			$ 112,500,000
Newmark [Member] \| Subsequent Event [Member] \| Fannie Mae [Member]
Subsequent Event [Line Items]
Proceeds from withdrew of cash pledge							$ 252,000,000
Newmark [Member] \| Subsequent Event [Member] \| Class A Common Stock [Member]
Subsequent Event [Line Items]
Dividend declared per share					$ 0.09
Dividend payable declared date					Oct. 24, 2018
Dividend payable, date to be paid					Nov. 28, 2018
Dividend payable record date					Nov. 07, 2018
Newmark [Member] \| Subsequent Event [Member] \| Class B Common Stock [Member]
Subsequent Event [Line Items]
Dividend declared per share					$ 0.09
Dividend payable declared date					Oct. 24, 2018
Dividend payable, date to be paid					Nov. 28, 2018
Dividend payable record date					Nov. 07, 2018
Newmark Partners L.P [Member] \| 5.375% Senior Notes Due 2019 [Member] \| Scenario Forecast [Member]
Subsequent Event [Line Items]
Repayments of outstanding borrowings	$ 300,000,000
Newmark Partners L.P [Member] \| Subsequent Event [Member] \| 5.375% Senior Notes Due 2019 [Member]
Subsequent Event [Line Items]
Stated interest rate				5.375%
Debt maturity year				2019
Redemption date				Dec. 05, 2018
Redemption description				The redemption of the 5.375% Senior Notes will occur on December 5, 2018 (the “Redemption Date”). The redemption price will be equal to the sum of the remaining scheduled payments of principal and interest as of the Redemption Date, discounted to the Redemption Date on a semi-annual basis (assuming a 360-day year consisting of twelve 30-day months) using a discount rate equal to the Treasury Rate (as defined in the indenture governing the 5.375% Senior Notes) plus 50 basis points. The redemption price will be calculated on the third business day prior to the Redemption Date. Newmark will repay the $300.0 million outstanding principal amount under the 2019 Promissory Note on the earlier of the spin-off date or December 5, 2018, using primarily proceeds from the sale of its 6.125% Senior Notes.
Newmark Partners L.P [Member] \| Subsequent Event [Member] \| 5.375% Senior Notes Due 2019 [Member] \| Treasury Rate [Member]
Subsequent Event [Line Items]
Debt instrument redemption discount rate basis spread				0.50%