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Restricted Securities Available for Sale (Schedule of Restricted Securities Available for Sale) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Restricted Cash and Cash Equivalents Items [Line Items]
Cost	$ 52.8cacc_RestrictedAvailableForSaleSecuritiesAmortizedCost	$ 53.3cacc_RestrictedAvailableForSaleSecuritiesAmortizedCost
Gross Unrealized Gains	0.2us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax	0.1us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
Gross Unrealized Losses	0us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax	(0.2)us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
Estimated Fair Value	53.0us-gaap_AvailableForSaleSecuritiesRestricted	53.2us-gaap_AvailableForSaleSecuritiesRestricted
US Government and Agency Securities [Member]
Restricted Cash and Cash Equivalents Items [Line Items]
Cost	21.8cacc_RestrictedAvailableForSaleSecuritiesAmortizedCost / us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsAxis = us-gaap_USGovernmentCorporationsAndAgenciesSecuritiesMember	28.8cacc_RestrictedAvailableForSaleSecuritiesAmortizedCost / us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsAxis = us-gaap_USGovernmentCorporationsAndAgenciesSecuritiesMember
Gross Unrealized Gains	0.2us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax / us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsAxis = us-gaap_USGovernmentCorporationsAndAgenciesSecuritiesMember	0.1us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax / us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsAxis = us-gaap_USGovernmentCorporationsAndAgenciesSecuritiesMember
Gross Unrealized Losses	0us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax / us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsAxis = us-gaap_USGovernmentCorporationsAndAgenciesSecuritiesMember	(0.1)us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax / us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsAxis = us-gaap_USGovernmentCorporationsAndAgenciesSecuritiesMember
Estimated Fair Value	22.0us-gaap_AvailableForSaleSecuritiesRestricted / us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsAxis = us-gaap_USGovernmentCorporationsAndAgenciesSecuritiesMember	28.8us-gaap_AvailableForSaleSecuritiesRestricted / us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsAxis = us-gaap_USGovernmentCorporationsAndAgenciesSecuritiesMember
Corporate Bond Securities [Member]
Restricted Cash and Cash Equivalents Items [Line Items]
Cost	21.0cacc_RestrictedAvailableForSaleSecuritiesAmortizedCost / us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsAxis = us-gaap_CorporateBondSecuritiesMember	19.1cacc_RestrictedAvailableForSaleSecuritiesAmortizedCost / us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsAxis = us-gaap_CorporateBondSecuritiesMember
Gross Unrealized Gains	0us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax / us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsAxis = us-gaap_CorporateBondSecuritiesMember	0us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax / us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsAxis = us-gaap_CorporateBondSecuritiesMember
Gross Unrealized Losses	0us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax / us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsAxis = us-gaap_CorporateBondSecuritiesMember	(0.1)us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax / us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsAxis = us-gaap_CorporateBondSecuritiesMember
Estimated Fair Value	21.0us-gaap_AvailableForSaleSecuritiesRestricted / us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsAxis = us-gaap_CorporateBondSecuritiesMember	19.0us-gaap_AvailableForSaleSecuritiesRestricted / us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsAxis = us-gaap_CorporateBondSecuritiesMember
Asset-backed Securities [Member]
Restricted Cash and Cash Equivalents Items [Line Items]
Cost	6.2cacc_RestrictedAvailableForSaleSecuritiesAmortizedCost / us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsAxis = us-gaap_AssetBackedSecuritiesMember	4.8cacc_RestrictedAvailableForSaleSecuritiesAmortizedCost / us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsAxis = us-gaap_AssetBackedSecuritiesMember
Gross Unrealized Gains	0us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax / us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsAxis = us-gaap_AssetBackedSecuritiesMember	0us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax / us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsAxis = us-gaap_AssetBackedSecuritiesMember
Gross Unrealized Losses	0us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax / us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsAxis = us-gaap_AssetBackedSecuritiesMember
Estimated Fair Value	6.2us-gaap_AvailableForSaleSecuritiesRestricted / us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsAxis = us-gaap_AssetBackedSecuritiesMember	4.8us-gaap_AvailableForSaleSecuritiesRestricted / us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsAxis = us-gaap_AssetBackedSecuritiesMember
Collateralized Mortgage Backed Securities [Member]
Restricted Cash and Cash Equivalents Items [Line Items]
Cost	3.8cacc_RestrictedAvailableForSaleSecuritiesAmortizedCost / us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsAxis = us-gaap_MortgageBackedSecuritiesMember	0.6cacc_RestrictedAvailableForSaleSecuritiesAmortizedCost / us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsAxis = us-gaap_MortgageBackedSecuritiesMember
Gross Unrealized Gains	0us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax / us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsAxis = us-gaap_MortgageBackedSecuritiesMember	0us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax / us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsAxis = us-gaap_MortgageBackedSecuritiesMember
Gross Unrealized Losses	0us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax / us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsAxis = us-gaap_MortgageBackedSecuritiesMember	0us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax / us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsAxis = us-gaap_MortgageBackedSecuritiesMember
Estimated Fair Value	$ 3.8us-gaap_AvailableForSaleSecuritiesRestricted / us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsAxis = us-gaap_MortgageBackedSecuritiesMember	$ 0.6us-gaap_AvailableForSaleSecuritiesRestricted / us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsAxis = us-gaap_MortgageBackedSecuritiesMember

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Restricted Available For Sale Securities Amortized Cost

+ References

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- Definition

Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (b)

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Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (c)

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- 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

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-Name Accounting Standards Codification

-Topic 235

-SubTopic 10

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-Paragraph 1

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



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