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Summary of Significant Accounting Policies - Reconciliation of Numerators and Denominators of EPS Calculation (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2015	Mar. 31, 2014	Mar. 31, 2013
Accounting Policies [Abstract]
Net loss	$ (3,363)us-gaap_NetIncomeLoss	$ (6,353)us-gaap_NetIncomeLoss	$ (25,423)us-gaap_NetIncomeLoss	$ (13,517)us-gaap_NetIncomeLoss	$ (22,705)us-gaap_NetIncomeLoss	$ (8,417)us-gaap_NetIncomeLoss	$ (14,623)us-gaap_NetIncomeLoss	$ (10,513)us-gaap_NetIncomeLoss	$ (48,656)us-gaap_NetIncomeLoss	$ (56,258)us-gaap_NetIncomeLoss	$ (66,131)us-gaap_NetIncomeLoss
Weighted-average shares of common stock outstanding									8,559amsc_WeightedAverageSharesOfCommonStockOutstanding	6,411amsc_WeightedAverageSharesOfCommonStockOutstanding	5,354amsc_WeightedAverageSharesOfCommonStockOutstanding
Weighted-average shares subject to repurchase									(82)us-gaap_WeightedAverageNumberOfSharesCommonStockSubjectToRepurchaseOrCancellation	(149)us-gaap_WeightedAverageNumberOfSharesCommonStockSubjectToRepurchaseOrCancellation	(47)us-gaap_WeightedAverageNumberOfSharesCommonStockSubjectToRepurchaseOrCancellation
Shares used in per-share calculation basic									8,477us-gaap_WeightedAverageNumberOfSharesOutstandingBasic	6,262us-gaap_WeightedAverageNumberOfSharesOutstandingBasic	5,307us-gaap_WeightedAverageNumberOfSharesOutstandingBasic
Shares used in per-share calculation diluted									8,477us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding	6,262us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding	5,307us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding
Basic	$ (0.36)us-gaap_EarningsPerShareBasic	$ (0.72)us-gaap_EarningsPerShareBasic	$ (3.12)us-gaap_EarningsPerShareBasic	$ (1.74)us-gaap_EarningsPerShareBasic	$ (3.30)us-gaap_EarningsPerShareBasic	$ (1.35)us-gaap_EarningsPerShareBasic	$ (2.39)us-gaap_EarningsPerShareBasic	$ (1.80)us-gaap_EarningsPerShareBasic	$ (5.74)us-gaap_EarningsPerShareBasic	$ (8.98)us-gaap_EarningsPerShareBasic	$ (12.46)us-gaap_EarningsPerShareBasic
Diluted	$ (0.36)us-gaap_EarningsPerShareDiluted	$ (0.72)us-gaap_EarningsPerShareDiluted	$ (3.12)us-gaap_EarningsPerShareDiluted	$ (1.74)us-gaap_EarningsPerShareDiluted	$ (3.30)us-gaap_EarningsPerShareDiluted	$ (1.35)us-gaap_EarningsPerShareDiluted	$ (2.39)us-gaap_EarningsPerShareDiluted	$ (1.80)us-gaap_EarningsPerShareDiluted	$ (5.74)us-gaap_EarningsPerShareDiluted	$ (8.98)us-gaap_EarningsPerShareDiluted	$ (12.46)us-gaap_EarningsPerShareDiluted

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