Discontinued Operations - Components of Consolidated Net Income (Loss) From Discontinued Operations (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($)
Other income (losses), net:
Consolidated net income (loss) from discontinued operations, net of tax	$ 178,462
Less: Net income (loss) from discontinued operations attributable to noncontrolling interest in subsidiaries	53,121
Newmark [Member]
Revenues:
Commissions	1,112,629
Gains from mortgage banking activities/originations, net	160,688
Real estate management and other services	375,428
Servicing fees	119,587
Fees from related parties	1,055
Interest income	35,238
Other revenues	607
Total revenues	1,805,232
Expenses:
Compensation and employee benefits	1,049,903
Equity-based compensation and allocations of net income to limited partnership units and FPUs	141,965
Total compensation and employee benefits	1,191,868
Occupancy and equipment	69,368
Fees to related parties	15,999
Professional and consulting fees	31,699
Communications	11,328
Selling and promotion	54,650
Commissions and floor brokerage	1,087
Interest expense	79,732
Other expenses	197,144
Total expenses	1,652,875
Other income (losses), net:
Gains (losses) on equity method investments	2,759
Other income (loss)	110,145
Total other income (losses), net	112,904
Income (loss) from operations before income taxes	265,261
Provision (benefit) for income taxes	86,799
Consolidated net income (loss) from discontinued operations, net of tax	178,462
Less: Net income (loss) from discontinued operations attributable to noncontrolling interest in subsidiaries	53,121
Net income (loss) from discontinued operations available to common stockholders	$ 125,341