Discontinued Operations - Components of Consolidated Net Income (Loss) From Discontinued Operations (Detail) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2018
Other income (losses), net:
Consolidated net income (loss) from discontinued operations, net of tax	$ 17,631	$ 42,390
Less: Net income (loss) from discontinued operations attributable to noncontrolling interest in subsidiaries	2,429	12,412
Newmark [Member]
Revenues:
Commissions	279,833	540,575
Gains from mortgage banking activities/originations, net	41,878	80,792
Real estate management and other services	107,121	203,999
Servicing fees	32,333	61,259
Fees from related parties	337	628
Interest income	7,426	13,499
Other revenues	105	153
Total revenues	469,033	900,905
Expenses:
Compensation and employee benefits	268,461	532,661
Equity-based compensation and allocations of net income to limited partnership units and FPUs	64,262	82,869
Total compensation and employee benefits	332,723	615,530
Occupancy and equipment	18,063	35,700
Fees to related parties	4,005	7,718
Professional and consulting fees	6,917	15,090
Communications	3,414	6,865
Selling and promotion	15,045	28,669
Commissions and floor brokerage	278	458
Interest expense	17,413	35,183
Other expenses	51,759	103,012
Total expenses	449,617	848,225
Other income (losses), net:
Gains (losses) on equity method investments	1,843	5,020
Other income (loss)	(2,291)	240
Total other income (losses), net	(448)	5,260
Income (loss) from operations before income taxes	18,968	57,940
Provision (benefit) for income taxes	1,337	15,550
Consolidated net income (loss) from discontinued operations, net of tax	17,631	42,390
Less: Net income (loss) from discontinued operations attributable to noncontrolling interest in subsidiaries	2,429	12,412
Net income (loss) from discontinued operations available to common stockholders	$ 15,202	$ 29,978