Employee Incentive and Retirement Plans - Stock-Based Compensation Expense Recorded in Consolidated Statement of Operations (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 73,639	$ 75,087	$ 70,983
Sales and marketing
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	6,095	7,362	7,654
Origination and servicing
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	3,155	4,322	4,804
Engineering and product development
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	19,860	20,478	22,047
Other general and administrative
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 44,529	$ 42,925	$ 36,478