Discontinued Operations - Components of Consolidated Net Income (Loss) From Discontinued Operations (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Other income (losses), net:
Consolidated net income (loss) from discontinued operations, net of tax	$ 176,169	$ 170,365
Less: Net income (loss) from discontinued operations attributable to noncontrolling interest in subsidiaries	52,353	(5,913)
Newmark [Member]
Revenues:
Commissions	1,116,935	1,014,741
Gains from mortgage banking activities/originations, net	160,688	205,999
Real estate management and other services	375,428	233,063
Servicing fees	119,587	110,441
Fees from related parties	1,055	1,373
Interest income	35,238	36,546
Other revenues	607	242
Total revenues	1,809,538	1,602,405
Expenses:
Compensation and employee benefits	1,052,487	1,007,173
Equity-based compensation and allocations of net income to limited partnership units and FPUs	141,965	111,917
Total compensation and employee benefits	1,194,452	1,119,090
Occupancy and equipment	69,368	62,448
Fees to related parties	15,999	13,208
Professional and consulting fees	31,699	34,270
Communications	11,328	11,809
Selling and promotion	54,650	52,443
Commissions and floor brokerage	1,087	956
Interest expense	79,732	25,546
Other expenses	197,144	128,417
Total expenses	1,655,459	1,448,187
Other income (losses), net:
Gains (losses) on equity method investments	2,759	1,562
Other income (loss)	110,145	72,081
Total other income (losses), net	112,904	73,643
Income (loss) from operations before income taxes	266,983	227,861
Provision (benefit) for income taxes	90,814	57,496
Consolidated net income (loss) from discontinued operations, net of tax	176,169	170,365
Less: Net income (loss) from discontinued operations attributable to noncontrolling interest in subsidiaries	52,353	(5,913)
Net income (loss) from discontinued operations available to common stockholders	$ 123,816	$ 176,278