Number of offices acquired.

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Percentage of voting equity interests acquired at the acquisition date in the business combination.

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Amount of consideration transferred, consisting of acquisition-date fair value of assets transferred by the acquirer, liabilities incurred by the acquirer, and equity interest issued by the acquirer.

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Amount of liability recognized arising from contingent consideration in a business combination, expected to be settled beyond one year or the normal operating cycle, if longer.

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Acquisitions - Additional Information (Detail) $ in Thousands							9 Months Ended	12 Months Ended
	Sep. 08, 2017 USD ($)	Sep. 07, 2017 Office	Jul. 26, 2017	Feb. 28, 2017	Dec. 15, 2016	Nov. 04, 2016	Sep. 30, 2017 USD ($)	Dec. 31, 2016 USD ($)
Business Acquisition [Line Items]
Total consideration transferred							$ 1,000,000	$ 139,000
Business acquisition, contingent cash consideration							13,700	28,100
Additional goodwill recognized							74,322	$ 37,100
Measurement period adjustments							(16,276)
Cantor [Member]
Business Acquisition [Line Items]
Noncontrolling interest			25.00%
BPF [Member]
Business Acquisition [Line Items]
Total consideration transferred	$ 875,000
Business acquistion price paid in units	$ 3,200
Business acquisition date	Sep. 08, 2017
Business acquisition, deferred tax asset							$ 99,100
Besso [Member]
Business Acquisition [Line Items]
Business acquisition date				Feb. 28, 2017
Sunrise Brokers [Member]
Business Acquisition [Line Items]
Business acquisition date					Dec. 15, 2016
Lucera [Member]
Business Acquisition [Line Items]
Business acquisition date						Nov. 04, 2016
Ownership percentage acquired						80.00%
Integra Realty Resources [Member]
Business Acquisition [Line Items]
Business acquisition date		Sep. 07, 2017
Number of offices acquired \| Office		6
Commercial Real Estate Consulting Firm [Member]
Business Acquisition [Line Items]
Business acquisition date			Jul. 26, 2017
Ownership percentage acquired			50.00%