Summary of Significant Accounting Policies - Schedule of Recognized Revenues (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Segment Reporting Information [Line Items]
Revenues	$ 430,460	$ 332,582
Leasing and Other Commissions [Member]
Segment Reporting Information [Line Items]
Revenues	159,371	127,567
Capital Markets [Member]
Segment Reporting Information [Line Items]
Revenues	101,364	77,391
Gains From Mortgage Banking Activities Origination Net [Member]
Segment Reporting Information [Line Items]
Revenues	38,914	45,262
Management Services, Servicing Fees and Other [Member]
Segment Reporting Information [Line Items]
Revenues	$ 130,811	$ 82,362