Fair Value Of Financial Instruments (Schedule Of Comparison Of The Carrying Value And Estimated Fair Value Of These Financial Instruments) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	$ 5.6	$ 4.2
Restricted cash and cash equivalents	146.6	111.3
Restricted securities available for sale	52.3	53.6
Net investment in Loans receivable	2,330.1	2,226.7
Revolving secured line of credit	115.9	102.8
Secured financing	1,143.9	938.9
Carrying Amount [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	5.6	4.2
Restricted cash and cash equivalents	146.6	111.3
Restricted securities available for sale	52.3	53.6
Net investment in Loans receivable	2,318.0	2,212.8
Revolving secured line of credit	115.9	102.8
Secured financing	1,138.6	935.6
Estimated Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	5.6	4.2
Restricted cash and cash equivalents	146.6	111.3
Restricted securities available for sale	52.3	53.6
Net investment in Loans receivable	2,330.1	2,226.7
Revolving secured line of credit	115.9	102.8
Secured financing	1,143.9	938.9
Mortgages [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Notes	3.7	3.8
Mortgages [Member] \| Carrying Amount [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Notes	3.7	3.8
Mortgages [Member] \| Estimated Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Notes	3.7	3.8
Senior Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Notes	313.1	367.1
Senior Notes [Member] \| Carrying Amount [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Notes	300.0	350.2
Senior Notes [Member] \| Estimated Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Notes	$ 313.1	$ 367.1

Restricted Cash And Cash Equivalents, Fair Value Disclosure

No definition available.

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- Definition

Secured Financing Fair Value Disclosure

+ References

No definition available.

+ Details

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Namespace Prefix:	cacc_
Data Type:	xbrli:monetaryItemType
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Period Type:	instant

- Definition

The carrying amount of securities categorized neither as held-to-maturity nor trading which serve as security for borrowings or other arrangements.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 6

-Article 9

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 08

-Paragraph b

-Article 4

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 5

-URI http://asc.fasb.org/extlink&oid=28368275&loc=d3e5086-111524

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 235

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX210.4-08(b))

-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

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- Definition

Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Cash

-URI http://asc.fasb.org/extlink&oid=6506951

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Cash Equivalents

-URI http://asc.fasb.org/extlink&oid=6507016

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- Definition

Fair value portion of contractual arrangement with a lender under which borrowings can be made up to a specific amount at any point in time.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Line-of-Credit Arrangement

-URI http://asc.fasb.org/extlink&oid=6517033

+ Details

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- Definition

Fair value portion of loan receivable, including, but not limited to, mortgage loans held for investment, finance receivables held for investment, policy loans on insurance contracts.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Glossary Loan

-URI http://asc.fasb.org/extlink&oid=6517073

+ Details

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Namespace Prefix:	us-gaap_
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Balance Type:	debit
Period Type:	instant

- Definition

Fair value portion of notes payable.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 19, 20, 22

-Article 5

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.19,20,22)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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