Stated interest rate percentage when periodic interest is paid in cash.

No definition available.

Name:	am_CashInterestStatedPercentageRate
Namespace Prefix:	am_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Description of the basis upon which the Payment-In-Kind interest rate is determined.

+ References

No definition available.

+ Details

Name:	am_DebtInstrumentDescriptionOfPaymentInKindInterestRateBasis
Namespace Prefix:	am_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Parent company's estimated annual future cash interest payments expected to be funded by the entity.

+ References

No definition available.

+ Details

Name:	am_FutureAnnualCashInterestPayments
Namespace Prefix:	am_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Interest paid on parent company debt through dividend payments made by the entity to a direct or indirect parent company.

+ References

No definition available.

+ Details

Name:	am_InterestPaidOnParentCompanyDebt
Namespace Prefix:	am_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Interest rate differential between the loan's cash-based stated interest rate and the loan's payment-in-kind stated interest rate.

+ References

No definition available.

+ Details

Name:	am_PaymentInKindInterestRateSpread
Namespace Prefix:	am_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Stated interest rate when periodic interest is paid in the form of additional PIK toggle notes.

+ References

No definition available.

+ Details

Name:	am_PaymentInKindInterestStatedPercentageRate
Namespace Prefix:	am_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Face (par) amount of debt instrument at time of issuance.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 835

-SubTopic 30

-Section 45

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6451184&loc=d3e28551-108399

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 835

-SubTopic 30

-Section 55

-Paragraph 8

-URI http://asc.fasb.org/extlink&oid=34725769&loc=d3e28878-108400

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of paid and unpaid common stock dividends declared with the form of settlement in cash.

+ References

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

-Article 3

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 505

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.3-04)

-URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of cash inflow from the sale of other assets as part of operating activities.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 25

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3536-108585

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The amount of any current tax-related balances due to affiliates as of the date of each statement of financial position presented.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 740

-SubTopic 10

-Section 50

-Paragraph 17

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32809-109319

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

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Balance Type:	na
Period Type:	duration

- Details

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- Details

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- Details

Name:	us-gaap_RelatedPartyTransactionAxis=am_SeniorPaymentInKindToggleNotesMember
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Related Party Information (Transactions with Parent Companies and Other Affiliated Companies) - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended			0 Months Ended
	Feb. 28, 2014	Feb. 28, 2013	Feb. 28, 2015	Feb. 10, 2014
Related Party Transaction [Line Items]
Cash dividends paid to parent	$ 9,614us-gaap_DividendsCommonStockCash	$ 19,929us-gaap_DividendsCommonStockCash
Century Intermediate Holding Company [Member]
Related Party Transaction [Line Items]
Tax sharing arrangement, amounts due to (from) affiliates			1,846
Cash dividends paid to parent	75,420		38,073
Senior PIK Toggle Notes [Member] \| Century Intermediate Holding Company [Member]
Related Party Transaction [Line Items]
Cash dividends paid to parent				50,000
PIK interest description			PIK Interest (as defined below), which is the cash interest rate plus 75 basis points
Aggregate principal amount of an indirect parent company's Senior PIK Toggle notes				285,000
Cash interest rate percentage				9.75%
PIK interest rate percentage				10.50%
PIK interest rate spread				0.75%
Future annual PIK cash interest payments				27,800
Parent company interest payment funded by dividends paid to parent			28,208
HL and L Property Company [Member] \| Century Intermediate Holding Company [Member]
Related Party Transaction [Line Items]
Proceeds from sale of assets to affiliated company			$ 9,865