| Income Taxes - Components of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands | Dec. 31, 2020 | Dec. 31, 2019 | 
|---|---|---|
| Deferred tax assets | ||
| Impairments of lease assets and inventory | $ 184 | $ 644 | 
| Employee benefits | 751 | 724 | 
| Accrued losses on uncompleted contracts | 3,716 | 3,335 | 
| Stock based compensation expense | 225 | 312 | 
| Federal net operating losses | 19,345 | 14,885 | 
| State net operating losses | 3,620 | 1,678 | 
| R&D and other tax credits | 806 | 806 | 
| Other | 631 | 437 | 
| Total deferred tax assets | 29,278 | 22,821 | 
| Deferred tax liabilities | ||
| Property, plant and equipment and AHFS | (5,825) | (7,523) | 
| Prepaid insurance | (512) | (402) | 
| Total deferred tax liabilities | (6,337) | (7,925) | 
| Net deferred tax assets | 22,941 | 14,896 | 
| Valuation allowance | (23,054) | (15,086) | 
| Net deferred taxes | $ (113) | $ (190) | 
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- Definition Deferred tax assets, Accrued losses on uncompleted contracts. No definition available. 
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- Definition Deferred tax assets, impairments of lease assets and inventory. No definition available. 
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- Definition Deferred tax assets (liabilities), gross. No definition available. 
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- Definition Deferred tax liabilities, Property plant and equipment and asset held for sale. No definition available. 
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- Definition Amount of deferred tax liability attributable to taxable temporary differences. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef 
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- Definition Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences and carryforwards. Reference 1: http://www.xbrl.org/2003/role/disclosureRef 
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- References No definition available. 
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- Definition Amount before allocation of valuation allowances of deferred tax asset attributable to deductible operating loss carryforwards. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef 
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- Definition Amount before allocation of valuation allowances of deferred tax asset attributable to deductible state and local operating loss carryforwards. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef 
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- Definition Amount, before allocation of valuation allowance, of deferred tax asset attributable to deductible temporary differences, classified as other. Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef 
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- Definition Amount before allocation of valuation allowances of deferred tax asset attributable to deductible research tax credit carryforwards. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef 
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- Definition Amount, before allocation of valuation allowance, of deferred tax asset attributable to deductible temporary differences from employee benefits, classified as other. Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef 
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- Definition Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences from share-based compensation. Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef 
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- Definition Amount of deferred tax assets for which it is more likely than not that a tax benefit will not be realized. Reference 1: http://www.xbrl.org/2003/role/disclosureRef 
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- Definition Amount, after deferred tax asset, of deferred tax liability attributable to taxable differences without jurisdictional netting. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef 
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- References No definition available. 
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- Definition Amount of deferred tax consequences attributable to taxable temporary differences derived from prepaid expenses. No definition available. 
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