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

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Date when the acquirer obtains control of the acquiree, in CCYY-MM-DD format.

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

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

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

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Description of the payment terms of the debt instrument (for example, whether periodic payments include principal and frequency of payments) and discussion about any contingencies associated with the payment.

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

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

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

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

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The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

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The carrying value as of the balance sheet date of the current portion of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

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

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Number of new stock issued during the period.

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Amount of stock repurchase plan authorized.

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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.

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Subsequent Events - Additional Information (Detail) - USD ($)							3 Months Ended		6 Months Ended		12 Months Ended
	Aug. 08, 2018	Aug. 01, 2018	Jul. 20, 2018	Jul. 19, 2018	Jul. 18, 2018	Mar. 19, 2018	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017	Aug. 06, 2018	Jul. 31, 2018	Mar. 18, 2018	Sep. 08, 2017	Feb. 07, 2017	Jun. 26, 2012
Cantor [Member]
Subsequent Event [Line Items]
Approved loan amount							$ 0		$ 0						$ 150,000,000
8.375% Senior Notes [Member]
Subsequent Event [Line Items]
Stated interest rate							8.375%		8.375%		8.375%
Principal amount of notes							$ 240,000,000		$ 240,000,000
Debt instrument, periodic interest payment description									semi-annually
8.125% Senior Notes [Member]
Subsequent Event [Line Items]
Stated interest rate							8.125%		8.125%		8.125%
Principal amount of notes																	$ 112,500,000
Debt maturity year									2042
Revolving Credit Facility [Member] \| Cantor [Member]
Subsequent Event [Line Items]
Interest rate						1.00%
Stated interest rate							5.34%		5.34%
Principal amount of notes						$ 250,000,000								$ 150,000
Approved loan amount							$ 130,000,000		$ 130,000,000
One Month LIBOR [Member] \| Revolving Credit Facility [Member] \| Cantor [Member]
Subsequent Event [Line Items]
Stated interest rate							3.25%		3.25%
Subsequent Event [Member]
Subsequent Event [Line Items]
Company’s repurchase authorization		$ 300,000,000											$ 194,000,000
Subsequent Event [Member] \| 8.375% Senior Notes [Member]
Subsequent Event [Line Items]
Repayments of outstanding balance				$ 240,000,000
Stated interest rate				8.375%
Subsequent Event [Member] \| 5.375% Senior Notes Due 2023 [Member] \| Senior Unsecured Obligation [Member]
Subsequent Event [Line Items]
Stated interest rate				5.375%
Principal amount of notes				$ 450,000,000
Debt instrument, periodic interest payment description				semi-annually
Interest payment description				The notes bear interest semi-annually at a rate of 5.375% per annum, on each January 24 and July 24, beginning on January 24, 2019, and will mature on July 24, 2023
Senior Notes maturity date				Jul. 24, 2023
Subsequent Event [Member] \| 8.125% Senior Notes [Member]
Subsequent Event [Line Items]
Stated interest rate		8.125%
Debt maturity year		2042
Redemption of outstanding principal amount		$ 112,500,000
Subsequent Event [Member] \| 8.125% Senior Notes [Member] \| Senior Unsecured Obligation [Member]
Subsequent Event [Line Items]
Stated interest rate				8.125%
Subsequent Event [Member] \| Revolving Credit Facility [Member] \| Cantor [Member]
Subsequent Event [Line Items]
Principal amount of notes												$ 400,000,000	$ 250,000,000
Subsequent Event [Member] \| Intercompany Credit Agreement [Member]
Subsequent Event [Line Items]
Stated interest rate		6.50%
Approved loan amount		$ 112,500,000
Class A Common Stock [Member]
Subsequent Event [Line Items]
Common stock, issued during the period									25,951,473		1,994,670
Company’s repurchase authorization																$ 300,000,000
Class A Common Stock [Member] \| Subsequent Event [Member]
Subsequent Event [Line Items]
Dividend declared per share		$ 0.18
Dividend payable declared date		Aug. 01, 2018
Dividend payable, date to be paid		Sep. 05, 2018
Dividend payable record date		Aug. 20, 2018
Class A Common Stock [Member] \| Subsequent Event [Member] \| Controlled Equity Offerings [Member]
Subsequent Event [Line Items]
Common stock, issued during the period	1,100,000
Class B Common Stock [Member]
Subsequent Event [Line Items]
Common stock, issued during the period							0	0	0	0
Class B Common Stock [Member] \| Subsequent Event [Member]
Subsequent Event [Line Items]
Dividend declared per share		$ 0.18
Dividend payable declared date		Aug. 01, 2018
Dividend payable, date to be paid		Sep. 05, 2018
Dividend payable record date		Aug. 20, 2018
Newmark [Member] \| Subsequent Event [Member]
Subsequent Event [Line Items]
Company’s repurchase authorization		$ 200,000,000
Newmark [Member] \| Class A Common Stock [Member] \| Subsequent Event [Member]
Subsequent Event [Line Items]
Dividend declared per share		$ 0.09
Dividend payable declared date		Aug. 01, 2018
Dividend payable, date to be paid		Sep. 05, 2018
Dividend payable record date		Aug. 20, 2018
Newmark [Member] \| Class B Common Stock [Member] \| Subsequent Event [Member]
Subsequent Event [Line Items]
Dividend declared per share		$ 0.09
Dividend payable declared date		Aug. 01, 2018
Dividend payable, date to be paid		Sep. 05, 2018
Dividend payable record date		Aug. 20, 2018
Cantor Fitzgerald LP [Member] \| Subsequent Event [Member] \| Senior Credit Facility [Member]
Subsequent Event [Line Items]
Remaining senior credit facility					$ 120,000,000
Cantor Fitzgerald LP [Member] \| Subsequent Event [Member] \| One Month LIBOR [Member] \| Senior Credit Facility [Member]
Subsequent Event [Line Items]
Interest rate					3.25%
Bank of America [Member] \| Subsequent Event [Member] \| Revolving Credit Facility [Member]
Subsequent Event [Line Items]
Remaining senior credit facility					$ 82,900,000
Bank of America [Member] \| Subsequent Event [Member] \| One Month LIBOR [Member] \| Revolving Credit Facility [Member]
Subsequent Event [Line Items]
Interest rate					2.25%
Jackson & Cooksey, Inc. [Member] \| Subsequent Event [Member]
Subsequent Event [Line Items]
Business acquisition date			Jul. 20, 2018