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Income Tax - Additional Information (Detail) - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Income Taxes [Line Items] |  |  |
Future enacted income tax rate assumed for both Federal and state deferred tax calculations | 21.00% | 34.00% | 34.00%
Net operating loss carryforwards | $ 17,600 | $ 9,900 |
Unclaimed tax deductions | 14,500 |  |
Net deferred tax assets recognized | 0 |  |
Unrecognized tax benefits | 700 |  |
Accrued interest and penalties related to income taxes | $ 0 | $ 0 |
Income tax rate assumed for both State and Foreign deferred tax calculations | 21.00% | 34.00% | 34.00%
Investment tax credits carryforwards [Member] |  |  |
Income Taxes [Line Items] |  |  |
Investment tax credits | $ 2,655 |  |
Research [Member] |  |  |
Income Taxes [Line Items] |  |  |
Investment tax credits | $ 100 |  |
Research and development tax credits expiration period | 2038 |  |
Canada | Investment tax credits carryforwards [Member] |  |  |
Income Taxes [Line Items] |  |  |
Investment tax credits | $ 2,600 | $ 2,600 |
Canada | Non Capital Loss Carryforwards [Member] |  |  |
Income Taxes [Line Items] |  |  |
Investment tax credits | 123,300 | 120,400 |
UK |  |  |
Income Taxes [Line Items] |  |  |
Net operating loss carryforwards | $ 1,829 | $ 800 |

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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://fasb.org/us-gaap/role/ref/legacyRef -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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