Discontinued Operations - Components of Consolidated Net Income (Loss) From Discontinued Operations (Detail) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2018
Other income (losses), net:
Consolidated net income (loss) from discontinued operations, net of tax	$ 122,738	$ 165,128
Less: Net income (loss) from discontinued operations attributable to noncontrolling interest in subsidiaries	34,062	46,474
Newmark [Member]
Revenues:
Commissions	319,349	859,924
Gains from mortgage banking activities/originations, net	51,972	132,764
Real estate management and other services	101,881	305,880
Servicing fees	34,948	96,207
Fees from related parties	307	935
Interest income	13,076	26,575
Other revenues	79	232
Total revenues	521,612	1,422,517
Expenses:
Compensation and employee benefits	293,639	826,300
Equity-based compensation and allocations of net income to limited partnership units and FPUs	35,669	118,538
Total compensation and employee benefits	329,308	944,838
Occupancy and equipment	19,045	54,745
Fees to related parties	4,099	11,817
Professional and consulting fees	11,162	26,252
Communications	2,615	9,480
Selling and promotion	14,704	43,373
Commissions and floor brokerage	300	758
Interest expense	22,750	57,933
Other expenses	54,824	157,836
Total expenses	458,807	1,307,032
Other income (losses), net:
Gains (losses) on equity method investments	17	5,037
Other income (loss)	93,653	93,893
Total other income (losses), net	93,670	98,930
Income (loss) from operations before income taxes	156,475	214,415
Provision (benefit) for income taxes	33,737	49,287
Consolidated net income (loss) from discontinued operations, net of tax	122,738	165,128
Less: Net income (loss) from discontinued operations attributable to noncontrolling interest in subsidiaries	34,062	46,473
Net income (loss) from discontinued operations available to common stockholders	$ 88,676	$ 118,655