Long-Term Debt (Components Of Long-Term Debt) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Debt Instrument [Line Items]
Other debt at an average rate of 3.4%, due through 2025	$ 20,156us-gaap_OtherBorrowings	$ 21,149us-gaap_OtherBorrowings
Capitalized lease arrangements at an average rate of 5.4%, due through 2031	15,206us-gaap_CapitalLeaseObligations	10,850us-gaap_CapitalLeaseObligations
Long-term debt and capitalized lease arrangements	2,251,012us-gaap_DebtAndCapitalLeaseObligations	604,142us-gaap_DebtAndCapitalLeaseObligations
Less current portion	18,826	20,844
Long-term debt	2,232,186	583,298
Other debt, average rate	3.40%amsg_OtherBorrowingsAverageInterestRate
Capitalized lease arrangements, average rate	5.40%
Line of Credit [Member]
Debt Instrument [Line Items]
Long-term debt	0	252,500
Term Loan [Member]
Debt Instrument [Line Items]
Long-term debt	865,650	0
5.625% Senior Unsecured Notes due 2020 [Member] \| Senior Notes [Member]
Debt Instrument [Line Items]
Long-term debt	250,000	250,000
5.625% Senior Unsecured Notes due 2022 [Member] \| Senior Notes [Member]
Debt Instrument [Line Items]
Long-term debt	1,100,000	0
8.04% Senior Secured Notes due 2020 [Member] \| Senior Notes [Member]
Debt Instrument [Line Items]
Long-term debt	$ 0	$ 69,643

Capital Lease Obligations, Average Interest Rate

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- Definition

Other Borrowings, Average Interest Rate

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- Definition

Amount equal to the present value (the principal) at the beginning of the lease term of minimum lease payments during the lease term (excluding that portion of the payments representing executory costs such as insurance, maintenance, and taxes to be paid by the lessor, together with any profit thereon) net of payments or other amounts applied to the principal through the balance sheet date.

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- Definition

Sum of the carrying values as of the balance sheet date of all debt, including all short-term borrowings, long-term debt, and capital lease obligations.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.7-03.16)

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- Definition

Carrying amount of long-term debt, net of unamortized discount or premium, including current and noncurrent amounts. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ References

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 16

-Article 7

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-Name Accounting Standards Codification

-Topic 210

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- Definition

Amount of long-term debt and capital lease obligation due after one year or beyond the normal operating cycle, if longer.

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-Publisher FASB

-Name Accounting Standards Codification

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-Publisher SEC

-Name Staff Accounting Bulletin (SAB)

-Number Topic 6

-Section H

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Amount of long-term debt and capital leases due within one year or the normal operating cycle, if longer.

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- Definition

The carrying amount as of the balance sheet date for the aggregate of other miscellaneous borrowings owed by the reporting entity.

+ References

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-Publisher FASB

-Name Accounting Standards Codification

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