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Revenue Recognition - Additional Information (Detail) - USD ($) | 3 Months Ended | 12 Months Ended
--- | --- | ---
Mar. 31, 2021 | Dec. 31, 2020 | Sep. 30, 2020 | Jun. 30, 2020 | Mar. 31, 2020 | Dec. 31, 2019 | Sep. 30, 2019 | Jun. 30, 2019 | Mar. 31, 2021 | Mar. 31, 2020 | Mar. 31, 2019
Contract With Customer Assets And Liabilities [Line Items] |  |  |  |  |  |  |  |  |  |  |
Net sales | $ 25,671,000 | $ 27,154,000 | $ 27,954,000 | $ 16,710,000 | $ 23,082,000 | $ 25,286,000 | $ 21,643,000 | $ 20,593,000 | $ 97,489,000 | $ 90,604,000 | $ 91,831,000
Percentage of revenue from contracts recognized over time |  |  |  |  |  |  |  |  | 60.00% | 70.00% | 60.00%
Percentage of revenue from contracts recognized upon shipment |  |  |  |  |  |  |  |  | 40.00% | 30.00% | 40.00%
Revenue recognized included in contract liability |  |  |  |  |  |  |  |  | $ 20,833,000 |  |
Unbilled revenue (contract assets) |  |  |  |  |  |  |  |  | 5,402,000 |  |
Contract with customer liability increase in contract asset due to contract progress. |  |  |  |  |  |  |  |  | 29,836,000 |  |
Contract with customer liability offset by invoicing to customers. |  |  |  |  |  |  |  |  | 24,434,000 |  |
Customer deposits, current |  |  |  |  |  |  |  |  | 12,924,000 |  |
Contract with customer liability offset by new customer deposits |  |  |  |  |  |  |  |  | 7,909,000 |  |
Receivables billed but not paid under retainage provisions in its customer contracts | 3,747,000 |  |  |  | 2,016,000 |  |  |  | 3,747,000 | $ 2,016,000 |
Revenue remaining unsatisfied performance obligations amount | 137,567,000 |  |  |  |  |  |  |  | 137,567,000 |  |
Customer Deposit [Member] |  |  |  |  |  |  |  |  |  |  |
Contract With Customer Assets And Liabilities [Line Items] |  |  |  |  |  |  |  |  |  |  |
Contract liabilities | 1,603,000 |  |  |  | 3,660,000 |  |  |  | 1,603,000 | 3,660,000 |
Prepaid Expenses and Other Current Assets [Member] |  |  |  |  |  |  |  |  |  |  |
Contract With Customer Assets And Liabilities [Line Items] |  |  |  |  |  |  |  |  |  |  |
Capitalized costs, net of amortization | $ 39,000 |  |  |  | $ 45,000 |  |  |  | 39,000 | 45,000 |
Amortization expense |  |  |  |  |  |  |  |  | 600,000 | 169,000 | $ 168,000
Sudan [Member] |  |  |  |  |  |  |  |  |  |  |
Contract With Customer Assets And Liabilities [Line Items] |  |  |  |  |  |  |  |  |  |  |
Net sales |  |  |  |  |  |  |  |  | 0 | 0 | 0
Iran [Member] |  |  |  |  |  |  |  |  |  |  |
Contract With Customer Assets And Liabilities [Line Items] |  |  |  |  |  |  |  |  |  |  |
Net sales |  |  |  |  |  |  |  |  | 0 | 0 | 0
Syria [Member] |  |  |  |  |  |  |  |  |  |  |
Contract With Customer Assets And Liabilities [Line Items] |  |  |  |  |  |  |  |  |  |  |
Net sales |  |  |  |  |  |  |  |  | $ 0 | $ 0 | $ 0

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