Represents the percentage of exercise price above last reported sale price of the entity's common stock.

No definition available.

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Namespace Prefix:	amag_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Proceeds from Termination of Bond Hedge and Warrants

+ References

No definition available.

+ Details

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Namespace Prefix:	amag_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Exercise price per share or per unit of warrants or rights outstanding.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08.(i)(4))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

+ Details

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Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of hedged item in hedging relationship. Excludes hedged asset or liability.

+ References

No definition available.

+ Details

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

- Definition

The number of issuer's shares to which the option contract is indexed.

+ References

+ Details

Name:	us-gaap_OptionIndexedToIssuersEquityIndexedShares
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

Exercise or strike price stated in the contract for options indexed to the issuer's equity shares.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 40
-Section 50
-Paragraph 5
-Subparagraph (a)(2)
-URI http://asc.fasb.org/extlink&oid=6445032&loc=d3e90205-114008

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 480
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (f)(1)
-URI http://asc.fasb.org/extlink&oid=109262807&loc=d3e22047-110879

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	duration

- Definition

Price of a single share of a number of saleable stocks of a company.

+ References

No definition available.

+ Details

Name:	us-gaap_SharePrice
Namespace Prefix:	us-gaap_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	instant

- Details

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Namespace Prefix:
Data Type:	na
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- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_WarrantMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=amag_ConvertibleNotesDue2019Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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Debt - Convertible Bond Hedge and Warrant Transactions (Details) - USD ($) $ / shares in Units, $ in Thousands, shares in Millions	1 Months Ended		12 Months Ended
	May 31, 2017	Feb. 28, 2014	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Oct. 31, 2018	Sep. 30, 2017	Feb. 11, 2014
Debt Instrument [Line Items]
Exercise price (in dollars per share)		$ 27.09
Initial exercise price (in dollars per share)		$ 34.12
Exercise price above last reported sale price of common stock		70.00%
Sale price of common stock (in dollars per share)			$ 15.19			$ 21.50	$ 18.45	$ 20.07
Proceeds to settle warrants	$ 300		$ 0	$ 323	$ 0
Bond Option
Debt Instrument [Line Items]
Common stock covered under convertible bond hedge/warrants (in shares)			0.8
Warrants
Debt Instrument [Line Items]
Common stock covered under convertible bond hedge/warrants (in shares)			1.0
Convertible Notes Due 2019 \| Convertible Debt
Debt Instrument [Line Items]
Remaining principal amount of convertible notes			$ 21,400