Summary of Significant Accounting Policies - Additional Information (Details) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	May 31, 2014	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2013
Significant Accounting Policies [Line Items]
Risk-sharing arrangement term				10 years
SPE, assets		$ 48,000	$ 49,000
SPE, liabilities		$ 19,000	22,000
Incentive Plan, mandatory holding period before awards vest	3 years
Employee Stock Purchase Plan, percentage of common stock fair value that employees can purchase					85.00%
Employees maximum 401(k) contribution		100.00%
Employer matching contributions		$ 500	$ 600	$ 800
Future lease commitments with expiration date		$ 17,591
Minimum
Significant Accounting Policies [Line Items]
Percentage of losses assumed on pool of loans sold				1.00%
Incentive Plan, awards vesting period (in years)	3 years
Maximum
Significant Accounting Policies [Line Items]
Percentage of losses assumed on pool of loans sold				2.25%
Incentive Plan, awards vesting period (in years)	4 years