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Income Tax - Additional Information (Detail) - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Income Taxes [Line Items] |  |  |
Future enacted income tax rate assumed for both Federal and state deferred tax calculations | 21.00% | 21.00% | 21.00%
Net operating loss carryforwards | $ 34,800 | $ 25,300 |
Unclaimed tax deductions | 16,000 |  |
Net deferred tax assets recognized | 0 |  |
Unrecognized tax benefits | 800 |  |
Accrued interest and penalties related to income taxes | 0 | 0 |
Investment tax credits carryforwards [Member] |  |  |
Income Taxes [Line Items] |  |  |
Investment tax credits | 3,029 |  |
Research [Member] |  |  |
Income Taxes [Line Items] |  |  |
Investment tax credits | $ 300 |  |
Research and development tax credits expiration period | 2040 |  |
Canada | Investment tax credits carryforwards [Member] |  |  |
Income Taxes [Line Items] |  |  |
Investment tax credits | $ 2,800 | 2,900 |
Canada | Non Capital Loss Carryforwards [Member] |  |  |
Income Taxes [Line Items] |  |  |
Investment tax credits | 105,600 | 104,200 |
UK |  |  |
Income Taxes [Line Items] |  |  |
Net operating loss carryforwards | $ 3,236 | $ 2,700 |

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- Definition Amount, after allocation of valuation allowances and deferred tax liability, of deferred tax asset attributable to deductible differences and carryforwards, without jurisdictional netting. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32537-109319 + Details
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