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Business Segment And Geographic Information (Narrative) (Details) (USD $) | 12 Months Ended
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Mar. 31, 2013 MW segment customer | Mar. 31, 2012 customer | Mar. 31, 2011
Segment Reporting Information [Line Items] |  |  |
Number of reportable business segments | 2 |  |
Megawatts of drive trains and power ratings | 10 |  |
Stock-based compensation expense | $ 8,138,000 | $ 9,864,000 | $ 13,412,000
Restructuring and impairment charges | 7,900,000 | 9,200,000 |
Loss contingency accrual | 1,800,000 |  |
Write-off of advanced payment to The Switch |  | $ 20,551,000 |
Number of customers | 2 | 2 |
Inox Wind [Member] |  |  |
Segment Reporting Information [Line Items] |  |  |
Percentage of total revenue, by customer | 19.00% | 18.00% |
JCNE [Member] |  |  |
Segment Reporting Information [Line Items] |  |  |
Percentage of total revenue, by customer | 13.00% |  |
Doosan Heavy Industries [Member] |  |  |
Segment Reporting Information [Line Items] |  |  |
Percentage of total revenue, by customer |  | 11.00% |
Sinovel [Member] |  |  |
Segment Reporting Information [Line Items] |  |  |
Percentage of total revenue, by customer |  |  | 68.00%
Outside The United States [Member] |  |  |
Segment Reporting Information [Line Items] |  |  |
Percentage of total revenue, by geographical region | 85.00% | 72.00% | 93.00%

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