Summary Of Significant Accounting Policies (Narrative) (Details)		12 Months Ended
		Dec. 31, 2017 USD ($) portfolio_segment	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Summary Of Significant Accounting Policies [Line Items]
Number of Portfolio Segments | portfolio_segment		2
Number of Reportable Segments | portfolio_segment		1
Monthly fee charged Dealer in Portfolio Program		$ 599
One-time enrollment fee in program		$ 9,850
Percentage of first accelerated Dealer Holdback payment retained		50.00%
Percentage of enrollment fee of first accelerated dealer holdback payment		50.00%
Period after Consumer Loan assignment that Dealer Loans written off		120 months
Period after month of purchase that Purchased Loans written off		120 months
Unamortized Debt Issuance Costs		$ 20,900,000	$ 16,800,000
Threshold to determine likelihood of being sustained		50.00%
Employer matching contribution, match percentage		100.00%
Matching contribution		2.00%
Employer matching contribution, additional match percentage		50.00%
Additional matching contribution		4.00%
Maximum matching contribution		4.00%
Recognized compensation expense		$ 4,600,000	3,600,000	$ 3,100,000
Advertising expense		400,000	300,000	$ 300,000
Cash and Cash Equivalents [Member]
Summary Of Significant Accounting Policies [Line Items]
Uninsured cash and cash equivalents		7,800,000	14,300,000
Restricted Cash And Cash Equivalents [Member]
Summary Of Significant Accounting Policies [Line Items]
Uninsured cash and cash equivalents		$ 255,100,000	224,100,000
Building [Member]
Summary Of Significant Accounting Policies [Line Items]
Estimated useful lives		P40Y
Building Improvements [Member]
Summary Of Significant Accounting Policies [Line Items]
Estimated useful lives		P10Y
Data Processing Equipment [Member]
Summary Of Significant Accounting Policies [Line Items]
Estimated useful lives		P3Y
Software [Member]
Summary Of Significant Accounting Policies [Line Items]
Estimated useful lives		P5Y
Office Furniture And Equipment [Member]
Summary Of Significant Accounting Policies [Line Items]
Estimated useful lives		P7Y
Leasehold Improvements [Member]
Summary Of Significant Accounting Policies [Line Items]
Estimated useful lives		P7Y
Software Development [Member]
Summary Of Significant Accounting Policies [Line Items]
Estimated useful lives		P5Y
Secured financings [Member]
Summary Of Significant Accounting Policies [Line Items]
Unamortized Debt Issuance Costs	[1]	$ 15,000,000	9,700,000
Senior Notes [Member]
Summary Of Significant Accounting Policies [Line Items]
Unamortized Debt Issuance Costs		$ 5,900,000	$ 7,100,000

[1] Warehouse facilities and Term ABS financings.