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

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-Name Accounting Standards Codification
-Topic 230
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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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Number of new stock issued during the period.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
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Subsequent Events - Additional Information (Detail) - $ / shares			1 Months Ended	3 Months Ended		12 Months Ended
	May 02, 2018	May 01, 2018	May 01, 2018	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Class A Common Stock [Member]
Subsequent Event [Line Items]
Common stock, issued during the period				18,925,702		1,994,670
Class A Common Stock [Member] \| Subsequent Event [Member]
Subsequent Event [Line Items]
Dividend declared per share		$ 0.18	$ 0.18
Dividend payable declared date		May 01, 2018
Dividend payable, date to be paid		Jun. 05, 2018
Dividend payable record date		May 21, 2018
Class B Common Stock [Member]
Subsequent Event [Line Items]
Common stock, issued during the period				0	0
Class B Common Stock [Member] \| Subsequent Event [Member]
Subsequent Event [Line Items]
Dividend declared per share		$ 0.18	$ 0.18
Dividend payable declared date		May 01, 2018
Dividend payable, date to be paid		Jun. 05, 2018
Dividend payable record date		May 21, 2018
Newmark [Member] \| Class A Common Stock [Member] \| Subsequent Event [Member]
Subsequent Event [Line Items]
Dividend declared per share	$ 0.09
Dividend payable declared date	May 02, 2018
Dividend payable, date to be paid	Jun. 05, 2018
Dividend payable record date	May 21, 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	May 02, 2018
Dividend payable, date to be paid	Jun. 05, 2018
Dividend payable record date	May 21, 2018
Controlled Equity Offerings [Member] \| Class A Common Stock [Member]
Subsequent Event [Line Items]
Common stock, issued during the period			3,200,000