| Debt - Interest Expense (Details) - USD ($) $ in Thousands | 3 Months Ended | 9 Months Ended | ||
|---|---|---|---|---|
| Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2018 | Dec. 31, 2017 | |
| Debt Instrument [Line Items] | ||||
| Amortization of debt discount and debt issuance costs | $ 251 | $ 875 | ||
| Interest expense, total | $ 194 | $ 446 | 648 | 1,815 | 
| Convertible notes | ||||
| Debt Instrument [Line Items] | ||||
| Interest expense, debt | 131 | 251 | 397 | 940 | 
| Amortization of debt discount and debt issuance costs | $ 63 | $ 195 | $ 251 | $ 875 | 
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- Definition Amount of amortization expense attributable to debt discount (premium) and debt issuance costs. Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef 
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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. No definition available. 
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- Definition Amount of the cost of borrowed funds accounted for as interest expense. Reference 1: http://www.xbrl.org/2003/role/disclosureRef 
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- Definition Amount of the cost of borrowed funds accounted for as interest expense for debt. Reference 1: http://www.xbrl.org/2003/role/disclosureRef 
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- Details 
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