Description of Business (Percentage of Consumer Loans Assigned with FICO Score of Less Than 650 or No FICO Score) (Details)	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Percentage Of Contracts With FICO Score Lower Than 650 Or No FICO Score [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable, Credit Quality, Additional Information	0.956	0.958	0.961

Includes any additional disclosures related to the credit quality of financing receivables. This may include a description of a credit quality indicator or a description of how the internal risk ratings used by a company relate to the likelihood of loss.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 29
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953659-111524

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 30
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953664-111524

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Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration