Debt (Receivable-Backed Notes Payable) (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Receivable-backed notes payable - recourse	$ 94,904	$ 76,674
Receivable backed notes payable - non-recourse	341,856	382,257
Total receivable-backed debt	436,760	458,931
Principal Balance of Pledged/Secured Receivables	508,128	527,170
Recourse Receivable Backed Notes Payable [Member]
Debt Instrument [Line Items]
Receivable-backed notes payable - recourse	94,904	76,674
Principal Balance of Pledged/Secured Receivables	116,205	93,597
Non-Recourse Receivable Backed Notes Payable [Member]
Debt Instrument [Line Items]
Unamortized debt issuance costs	(5,515)	(6,807)
Receivable backed notes payable - non-recourse	341,856	382,257
Principal Balance of Pledged/Secured Receivables	391,923	433,573
Liberty Bank Facility [Member] | Recourse Receivable Backed Notes Payable [Member]
Debt Instrument [Line Items]
Receivable-backed notes payable - recourse	$ 28,247	$ 17,654
Interest Rate	5.25%	5.25%
Principal Balance of Pledged/Secured Receivables	$ 34,545	$ 22,062
NBA Receivables Facility [Member] | Recourse Receivable Backed Notes Payable [Member]
Debt Instrument [Line Items]
Receivable-backed notes payable - recourse	$ 35,809	$ 48,414
Interest Rate	4.79%	5.27%
Principal Balance of Pledged/Secured Receivables	$ 43,706	$ 57,805
Pacific Western Facility [Member] | Recourse Receivable Backed Notes Payable [Member]
Debt Instrument [Line Items]
Receivable-backed notes payable - recourse	$ 30,848	$ 10,606
Interest Rate	4.92%	5.52%
Principal Balance of Pledged/Secured Receivables	$ 37,954	$ 13,730
KeyBank/DZ Purchase Facility [Member] | Non-Recourse Receivable Backed Notes Payable [Member]
Debt Instrument [Line Items]
Receivable backed notes payable - non-recourse	$ 19,035
Interest Rate	4.84%
Principal Balance of Pledged/Secured Receivables	$ 23,390
Quorum Purchase Facility [Member] | Non-Recourse Receivable Backed Notes Payable [Member]
Debt Instrument [Line Items]
Receivable backed notes payable - non-recourse	44,865	40,074
Principal Balance of Pledged/Secured Receivables	50,337	45,283
2012 Term Securitization [Member] | Non-Recourse Receivable Backed Notes Payable [Member]
Debt Instrument [Line Items]
Receivable backed notes payable - non-recourse	$ 9,986	$ 15,212
Interest Rate	2.94%	2.94%
Principal Balance of Pledged/Secured Receivables	$ 11,558	$ 16,866
2013 Term Securitization [Member] | Non-Recourse Receivable Backed Notes Payable [Member]
Debt Instrument [Line Items]
Receivable backed notes payable - non-recourse	$ 20,090	$ 27,573
Interest Rate	3.20%	3.20%
Principal Balance of Pledged/Secured Receivables	$ 21,995	$ 29,351
2015 Term Securitization [Member] | Non-Recourse Receivable Backed Notes Payable [Member]
Debt Instrument [Line Items]
Receivable backed notes payable - non-recourse	$ 34,093	$ 44,230
Interest Rate	3.02%	3.02%
Principal Balance of Pledged/Secured Receivables	$ 36,676	$ 47,690
2016 Term Securitization [Member] | Non-Recourse Receivable Backed Notes Payable [Member]
Debt Instrument [Line Items]
Receivable backed notes payable - non-recourse	$ 52,632	$ 63,982
Interest Rate	3.35%	3.35%
Principal Balance of Pledged/Secured Receivables	$ 58,817	$ 72,590
2017 Term Securitization [Member] | Non-Recourse Receivable Backed Notes Payable [Member]
Debt Instrument [Line Items]
Receivable backed notes payable - non-recourse	$ 69,763	$ 83,513
Interest Rate	3.12%	3.12%
Principal Balance of Pledged/Secured Receivables	$ 79,551	$ 95,877
2018 Term Securitization [Member] | Non-Recourse Receivable Backed Notes Payable [Member]
Debt Instrument [Line Items]
Receivable backed notes payable - non-recourse	$ 96,907	$ 114,480
Interest Rate	4.02%	4.02%
Principal Balance of Pledged/Secured Receivables	$ 109,599	$ 125,916
Minimum [Member] | Quorum Purchase Facility [Member] | Non-Recourse Receivable Backed Notes Payable [Member]
Debt Instrument [Line Items]
Interest Rate	4.75%	4.75%
Maximum [Member] | Quorum Purchase Facility [Member] | Non-Recourse Receivable Backed Notes Payable [Member]
Debt Instrument [Line Items]
Interest Rate	5.50%	5.50%