Employee Incentive and Retirement 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, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation, net	$ 13,479	$ 10,537	$ 37,558	$ 25,889
Sales and marketing
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	2,048	912	5,373	5,029
Origination and servicing
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	817	599	2,405	1,427
General and administrative: | Engineering and product development
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	2,554	1,492	6,392	3,487
General and administrative: | Other
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	8,060	7,534	23,388	15,946
Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	8,101	6,996	23,314	19,484
ESPP
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	491	0	1,416	0
RSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	3,037	0	5,262	0
Stock issued related to acquisition
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 1,850	$ 3,541	$ 7,566	$ 6,405