Commitments, Contingencies and Guarantees - Narrative (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)	Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)	Dec. 31, 2017 USD ($)
Loss Contingencies [Line Items]
Number of consecutive periods	5		5
Renewal term (in years)	3 years		3 years
Rent expense	$ 812	$ 750	$ 1,556	$ 1,475
Unused commitments to extend credit	3,700		3,700
Restricted cash	142,542	$ 103,569	142,542	$ 103,569	$ 129,224
Collectibility of Receivables
Loss Contingencies [Line Items]
Loss contingency accrual	2,600		2,600
GS Holdings
Loss Contingencies [Line Items]
Tangible capital	7,500		7,500
Minimum aggregate net income, four fiscal quarters			$ 5,000
Maximum ratio of liabilities to equity			3.00
Financial Guarantee
Loss Contingencies [Line Items]
Restricted cash	72,700		$ 72,700
Guarantees, fair value	600		600
Contractual Restricted Cash Under Arrangement
Loss Contingencies [Line Items]
Restricted cash	42,200		42,200
Bank Partners
Loss Contingencies [Line Items]
Financing receivable, nonaccrual status	$ 14,200		$ 14,200