Debt (Receivable-Backed Notes Payable) (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Receivable-backed notes payable - recourse	$ 86,820	$ 76,674
Receivable backed notes payable - non-recourse	351,316	382,257
Total receivable-backed debt	438,136	458,931
Principal Balance of Pledged/Secured Receivables	510,923	527,170
Recourse Receivable Backed Notes Payable [Member]
Debt Instrument [Line Items]
Receivable-backed notes payable - recourse	86,820	76,674
Principal Balance of Pledged/Secured Receivables	106,783	93,597
Non-Recourse Receivable Backed Notes Payable [Member]
Debt Instrument [Line Items]
Unamortized debt issuance costs	(5,927)	(6,807)
Receivable backed notes payable - non-recourse	351,316	382,257
Principal Balance of Pledged/Secured Receivables	404,140	433,573
Liberty Bank Facility [Member] | Recourse Receivable Backed Notes Payable [Member]
Debt Instrument [Line Items]
Receivable-backed notes payable - recourse	$ 27,708	$ 17,654
Interest Rate	5.50%	5.25%
Principal Balance of Pledged/Secured Receivables	$ 34,152	$ 22,062
NBA Receivables Facility [Member] | Recourse Receivable Backed Notes Payable [Member]
Debt Instrument [Line Items]
Receivable-backed notes payable - recourse	$ 39,698	$ 48,414
Interest Rate	5.18%	5.27%
Principal Balance of Pledged/Secured Receivables	$ 48,487	$ 57,805
Pacific Western Facility [Member] | Recourse Receivable Backed Notes Payable [Member]
Debt Instrument [Line Items]
Receivable-backed notes payable - recourse	$ 19,414	$ 10,606
Interest Rate	5.34%	5.52%
Principal Balance of Pledged/Secured Receivables	$ 24,144	$ 13,730
KeyBank/DZ Purchase Facility [Member] | Non-Recourse Receivable Backed Notes Payable [Member]
Debt Instrument [Line Items]
Receivable backed notes payable - non-recourse	$ 14,436
Interest Rate	5.16%
Principal Balance of Pledged/Secured Receivables	$ 17,641
Quorum Purchase Facility [Member] | Non-Recourse Receivable Backed Notes Payable [Member]
Debt Instrument [Line Items]
Receivable backed notes payable - non-recourse	38,112	40,074
Principal Balance of Pledged/Secured Receivables	43,024	45,283
2012 Term Securitization [Member] | Non-Recourse Receivable Backed Notes Payable [Member]
Debt Instrument [Line Items]
Receivable backed notes payable - non-recourse	$ 11,431	$ 15,212
Interest Rate	2.94%	2.94%
Principal Balance of Pledged/Secured Receivables	$ 13,229	$ 16,866
2013 Term Securitization [Member] | Non-Recourse Receivable Backed Notes Payable [Member]
Debt Instrument [Line Items]
Receivable backed notes payable - non-recourse	$ 22,308	$ 27,573
Interest Rate	3.20%	3.20%
Principal Balance of Pledged/Secured Receivables	$ 24,494	$ 29,351
2015 Term Securitization [Member] | Non-Recourse Receivable Backed Notes Payable [Member]
Debt Instrument [Line Items]
Receivable backed notes payable - non-recourse	$ 37,109	$ 44,230
Interest Rate	3.02%	3.02%
Principal Balance of Pledged/Secured Receivables	$ 40,428	$ 47,690
2016 Term Securitization [Member] | Non-Recourse Receivable Backed Notes Payable [Member]
Debt Instrument [Line Items]
Receivable backed notes payable - non-recourse	$ 56,672	$ 63,982
Interest Rate	3.35%	3.35%
Principal Balance of Pledged/Secured Receivables	$ 63,830	$ 72,590
2017 Term Securitization [Member] | Non-Recourse Receivable Backed Notes Payable [Member]
Debt Instrument [Line Items]
Receivable backed notes payable - non-recourse	$ 74,396	$ 83,513
Interest Rate	3.12%	3.12%
Principal Balance of Pledged/Secured Receivables	$ 85,322	$ 95,877
2018 Term Securitization [Member] | Non-Recourse Receivable Backed Notes Payable [Member]
Debt Instrument [Line Items]
Receivable backed notes payable - non-recourse	$ 102,779	$ 114,480
Interest Rate	4.02%	4.02%
Principal Balance of Pledged/Secured Receivables	$ 116,172	$ 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%