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Revenue Recognition - Additional Information (Detail) - USD ($) | 3 Months Ended | 12 Months Ended |
--- | --- | --- | ---
Mar. 31, 2019 | Dec. 31, 2018 | Sep. 30, 2018 | Jun. 30, 2018 | Mar. 31, 2018 | Dec. 31, 2017 | Sep. 30, 2017 | Jun. 30, 2017 | Mar. 31, 2019 | Mar. 31, 2018 | Mar. 31, 2017 | Apr. 01, 2018
Contract With Customer Assets And Liabilities [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Net sales | $ 23,641,000 | $ 17,198,000 | $ 21,441,000 | $ 29,551,000 | $ 22,178,000 | $ 17,281,000 | $ 17,224,000 | $ 20,851,000 | $ 91,831,000 | $ 77,534,000 | $ 91,769,000 |
Percentage of revenue from contracts recognized over time |  |  |  |  |  |  |  |  | 60.00% |  |  |
Percentage of revenue from contracts recognized upon shipment |  |  |  |  |  |  |  |  | 40.00% |  |  |
Revenue recognized included in contract liability |  |  |  |  |  |  |  |  | $ 10,680,000 |  |  |
Unbilled revenue |  |  |  |  |  |  |  |  | 1,430,000 |  |  |
Contract with customer liability increase in contract asset due to contract progress. |  |  |  |  |  |  |  |  | 7,626,000 |  |  |
Contract with customer liability offset by invoicing to customers. |  |  |  |  |  |  |  |  | 5,894,000 |  |  |
Customer deposits, current |  |  |  |  |  |  |  |  | 4,262,000 |  |  |
Contract with customer liability offset by new customer deposits. | 16,875,000 |  |  |  |  |  |  |  | 16,875,000 |  |  |
Receivables billed but not paid under retainage provisions in its customer contracts | 2,214,000 |  |  |  | $ 1,124,000 |  |  |  | 2,214,000 | 1,124,000 |  |
Amortization expense |  |  |  |  |  |  |  |  | 168,000 |  |  |
Revenue remaining unsatisfied performance obligations amount | 132,127,000 |  |  |  |  |  |  |  | 132,127,000 |  |  |
Revenue remaining performance obligation held for sale | 8,039,000 |  |  |  |  |  |  |  | 8,039,000 |  |  |
Disposal Group, Held-for-sale, Not Discontinued Operations [Member] |  |  |  |  |  |  |  |  |  |  |  |
Contract With Customer Assets And Liabilities [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Unbilled revenue | 302,000 |  |  |  |  |  |  |  | 302,000 |  |  |
Customer deposits | 1,933,000 |  |  |  |  |  |  |  | 1,933,000 |  |  |
Customer Deposit [Member] |  |  |  |  |  |  |  |  |  |  |  |
Contract With Customer Assets And Liabilities [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Contract liabilities | 6,382,000 |  |  |  |  |  |  |  | 6,382,000 |  |  | $ 2,220,000
Prepaid Expenses and Other Current Assets [Member] |  |  |  |  |  |  |  |  |  |  |  |
Contract With Customer Assets And Liabilities [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Capitalized costs, net of amortization | $ 133,000 |  |  |  |  |  |  |  | 133,000 |  |  | $ 118,000
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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