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Income Tax - Significant Components of Company's Deferred Tax Assets and Deferred Tax Liabilities (Detail) - USD ($) $ in Thousands | Dec. 31, 2020 | Dec. 31, 2019
--- | --- | ---
Deferred tax assets |  |
Tax basis in excess of book value of assets | $ 892 | $ 891
Non-capital loss carryforwards | 35,596 | 33,166
Research and development deductions and credits | 7,010 | 6,256
Stock options | 466 | 315
§59(e) Capitalized R&D expenses | 3,757 | 3,501
Accrued expenses | 164 | 79
Other | 183 | 181
Total deferred tax assets | 48,068 | 44,389
Valuation allowance | (47,539) | (43,875)
Net deferred assets | 529 | 514
Deferred tax liabilities |  |
Right of use assets | (135) | (79)
Other | (394) | (435)
Total deferred tax liabilities | (529) | $ (514)
Net deferred tax assets | $ 0 |

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