Employee Incentive Plans - Schedule of Stock-Based Compensation Expense Recorded for Stock Options, Warrants and Series F Convertible Preferred Stock (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 17,801	$ 19,498
Sales and marketing
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	1,860	2,299
Origination and servicing
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	1,072	1,416
Engineering and product development
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	5,279	6,588
Other general and administrative
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	9,590	9,195
Stock issued related to acquisition
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	0	134
Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	2,567	4,345
RSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	14,793	14,634
ESPP
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 441	$ 385