Employee Incentive and Retirement Plans - Restructuring (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Restructuring Cost and Reserve [Line Items]
Severance expense	$ 0	$ 2,730,000	$ 0
Sales and marketing
Restructuring Cost and Reserve [Line Items]
Severance expense		772,000
Origination and servicing
Restructuring Cost and Reserve [Line Items]
Severance expense		1,174,000
Engineering and product development
Restructuring Cost and Reserve [Line Items]
Severance expense		134,000
Other general and administrative
Restructuring Cost and Reserve [Line Items]
Severance expense		$ 650,000