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, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation, net	$ 11,593	$ 7,033
Sales and marketing
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	1,519	3,502
Origination and servicing
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	721	358
General and administrative: | Engineering and product development
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	1,406	737
General and administrative: | Other
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	7,947	2,436
Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	7,086	7,033
Available for ESPP
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	479	0
RSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	481	0
Springstone Financial, Llc
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 3,547	$ 0