Fair Value Measurements (Schedule Of Items Measured At Fair Value On A Recurring Basis) (Details) (USD $) In Thousands, unless otherwise specified	Nov. 30, 2014	Feb. 28, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market securities	$ 202,540	$ 641,622
Mutual fund investments	9,221us-gaap_TradingSecurities	5,609us-gaap_TradingSecurities
Derivative instruments	191us-gaap_DerivativeAssets
Total assets at fair value	211,952us-gaap_AssetsFairValueDisclosure	647,231us-gaap_AssetsFairValueDisclosure
Percent of total assets at fair value	100.00%	100.00%
Percent of total assets	1.70%kmx_ItemAsPercentageOfTotalAssets	5.50%kmx_ItemAsPercentageOfTotalAssets
Derivative instruments	3,298us-gaap_DerivativeLiabilities	1,351us-gaap_DerivativeLiabilities
Total liabilities at fair value	3,298us-gaap_LiabilitiesFairValueDisclosure	1,351us-gaap_LiabilitiesFairValueDisclosure
Percent of total liabilities	0.00%kmx_ItemAsPercentageOfTotalLiabilities	0.00%kmx_ItemAsPercentageOfTotalLiabilities
Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market securities	202,540	641,622
Mutual fund investments	9,221	5,609
Derivative instruments	0
Total assets at fair value	211,761	647,231
Percent of total assets at fair value	99.90%	100.00%
Percent of total assets	1.70%	5.50%
Derivative instruments	0	0
Total liabilities at fair value	0	0
Percent of total liabilities	0.00%	0.00%
Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market securities	0	0
Mutual fund investments	0	0
Derivative instruments	191
Total assets at fair value	191	0
Percent of total assets at fair value	0.10%	0.00%
Percent of total assets	0.00%	0.00%
Derivative instruments	3,298	1,351
Total liabilities at fair value	$ 3,298	$ 1,351
Percent of total liabilities	0.00%	0.00%

Item as percentage of total assets

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Item as percentage of total assets at fair value

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Item as percentage of total liabilities

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- Definition

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 820

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (a)

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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

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-Name Accounting Standards Codification

-Glossary Cash Equivalents

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Fair value, after the effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets not subject to a master netting arrangement and not elected to be offset.

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-Topic 210

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-Paragraph 3

-Subparagraph (c)

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Fair value, after the effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities not subject to a master netting arrangement and not elected to be offset.

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Fair value of financial and nonfinancial obligations.

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- Definition

Amount of investments in debt and equity securities and other forms of securities that provide ownership interests classified as trading.

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

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-Name Accounting Standards Codification

-Topic 942

-SubTopic 210

-Section S99

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-Subparagraph (SX 210.9-03.4)

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