Warrant instruments, fair value disclosure.

No definition available.

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- 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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- Definition

Expected dividends to be paid to holders of the underlying shares or financial instruments (expressed as a percentage of the share or instrument's price).

+ 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 (bbb)
-URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258

+ Details

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- Definition

Period the instrument, asset or liability is expected to be outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

+ Details

Name:	us-gaap_FairValueAssumptionsExpectedTerm
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- Definition

Measure of dispersion, in percentage terms (for instance, the standard deviation or variance), for a given stock price.

+ References

+ Details

Name:	us-gaap_FairValueAssumptionsExpectedVolatilityRate
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- Definition

Risk-free interest rate assumption used in valuing an instrument.

+ References

+ Details

Name:	us-gaap_FairValueAssumptionsRiskFreeInterestRate
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Data Type:	num:percentItemType
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- Details

Name:	us-gaap_ClassOfWarrantOrRightAxis=amsc_NovemberTwoThousandFourteenWarrantMember
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Warrants and Derivative Liabilities - Schedule of Assumptions Used to Calculate the Fair Value of Warrants (Detail) - USD ($) $ in Millions		3 Months Ended
	Sep. 25, 2017	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015
Derivative [Line Items]
Risk-free interest rate	1.09%			1.09%
Expected annual dividend yield	0.00%			0.00%
Expected volatility	65.71%			66.54%
Term (years)	3 months 27 days			3 months 22 days
Fair value	$ 0.6			$ 0.4
November 2014 warrant
Derivative [Line Items]
Risk-free interest rate		2.20%	1.87%	1.49%	1.44%	1.41%	1.43%	0.93%	0.77%	0.98%	1.51%	1.17%	1.44%	1.28%
Expected annual dividend yield		0.00%	0.00%	0.00%	0.00%	0.00%	0.00%	0.00%	0.00%	0.00%	0.00%	0.00%	0.00%	0.00%
Expected volatility		65.86%	65.86%	65.64%	67.21%	66.53%	69.31%	68.96%	70.01%	69.88%	70.02%	73.02%	74.18%	75.96%
Term (years)		1 year 7 months 13 days	1 year 10 months 13 days	2 years 1 month 13 days	2 years 4 months 13 days	2 years 7 months 13 days	2 years 10 months 13 days	3 years 1 month 13 days	3 years 4 months 13 days	3 years 7 months 13 days	3 years 10 months 13 days	4 years 1 month 13 days	4 years 4 months 13 days	4 years 7 months 13 days
Fair value		$ 1.1	$ 0.4	$ 0.8	$ 0.9	$ 1.8	$ 2.3	$ 2.3	$ 3.2	$ 2.6	$ 2.1	$ 1.3	$ 1.8	$ 2.5