Summary of Significant Accounting Policies - Schedule of Recognized Revenues (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Disaggregation Of Revenue [Line Items]
Revenues	$ 357,908	$ 319,340	$ 979,307	$ 859,908
Gains from mortgage banking activities/originations, net	72,332	51,972	148,769	132,763
Management services, servicing fees and other	156,394	147,497	457,692	423,217
Revenues	586,634	518,809	1,585,768	1,415,888
Leasing and Other Commissions [Member]
Disaggregation Of Revenue [Line Items]
Revenues	213,242	203,904	603,094	541,417
Capital Markets Commissions [Member]
Disaggregation Of Revenue [Line Items]
Revenues	$ 144,666	$ 115,436	$ 376,213	$ 318,491