Revenues from Contracts with Customers - Summary of Impact to Condensed Consolidated Statements of Operations (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Revenue Initial Application Period Cumulative Effect Transition [Line Items]
Leasing and other commissions	$ 159,371
Capital Markets	101,364
Gains from mortgage banking activities/originations, net	38,914	$ 45,262
Management services, servicing fees and other	130,811	82,362
Compensation and employee benefits	252,695	215,145
Operating, administrative and other	75,427	$ 47,382
ASC 606 [Member] | Under Previous U.S. GAAP [Member]
Revenue Initial Application Period Cumulative Effect Transition [Line Items]
Leasing and other commissions	148,754
Capital Markets	101,364
Gains from mortgage banking activities/originations, net	38,914
Management services, servicing fees and other	112,424
Compensation and employee benefits	247,053
Operating, administrative and other	57,040
ASC 606 [Member] | Effect of Change Higher/(Lower) [Member]
Revenue Initial Application Period Cumulative Effect Transition [Line Items]
Leasing and other commissions	10,617
Management services, servicing fees and other	18,387
Compensation and employee benefits	5,642
Operating, administrative and other	$ 18,387