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		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 16,106	$ 17,922	$ 54,692	$ 46,390
Sales and marketing
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	1,591	1,699	5,857	5,016
Origination and servicing
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	1,049	1,013	3,819	2,722
Engineering and product development
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	4,640	4,931	17,001	13,134
Other general and administrative
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	8,826	10,279	28,015	25,518
Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	3,435	6,208	11,927	17,632
RSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	12,295	11,143	41,451	25,044
ESPP
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	376	438	1,155	1,273
Stock issued related to acquisition
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 0	$ 133	$ 159	$ 2,441