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Income Tax - Summary of Investment Tax Credits and Non-Capital Losses and Net Operating Losses (Detail) - USD ($) $ in Thousands | Dec. 31, 2017 | Dec. 31, 2016
--- | --- | ---
Schedule Of Tax Credits And Losses Carry Forward Expiration [Line Items] |  |
Net Operating Losses | $ 9,900 | $ 1,300
UNITED KINGDOM |  |
Schedule Of Tax Credits And Losses Carry Forward Expiration [Line Items] |  |
Net Operating Losses | 849 | 200
US [Member] |  |
Schedule Of Tax Credits And Losses Carry Forward Expiration [Line Items] |  |
Net Operating Losses | 9,874 |
Investment tax credits carryforwards [Member] |  |
Schedule Of Tax Credits And Losses Carry Forward Expiration [Line Items] |  |
Investment tax credits | 2,603 |
Investment tax credits carryforwards [Member] | CANADA |  |
Schedule Of Tax Credits And Losses Carry Forward Expiration [Line Items] |  |
Investment tax credits | 2,600 | 2,600
Non Capital Loss Carryforwards [Member] | CANADA |  |
Schedule Of Tax Credits And Losses Carry Forward Expiration [Line Items] |  |
Investment tax credits | 120,400 | $ 115,900
Non-capital Losses | 120,423 |
2026 [Member] | Investment tax credits carryforwards [Member] |  |
Schedule Of Tax Credits And Losses Carry Forward Expiration [Line Items] |  |
Investment tax credits | 244 |
2026 [Member] | Non Capital Loss Carryforwards [Member] | CANADA |  |
Schedule Of Tax Credits And Losses Carry Forward Expiration [Line Items] |  |
Non-capital Losses | 7,335 |
2027 [Member] | Investment tax credits carryforwards [Member] |  |
Schedule Of Tax Credits And Losses Carry Forward Expiration [Line Items] |  |
Investment tax credits | 71 |
2027 [Member] | Non Capital Loss Carryforwards [Member] | CANADA |  |
Schedule Of Tax Credits And Losses Carry Forward Expiration [Line Items] |  |
Non-capital Losses | 4,949 |
2028 [Member] | Investment tax credits carryforwards [Member] |  |
Schedule Of Tax Credits And Losses Carry Forward Expiration [Line Items] |  |
Investment tax credits | 148 |
2028 [Member] | Non Capital Loss Carryforwards [Member] | CANADA |  |
Schedule Of Tax Credits And Losses Carry Forward Expiration [Line Items] |  |
Non-capital Losses | 8,020 |
2029 [Member] | UNITED KINGDOM |  |
Schedule Of Tax Credits And Losses Carry Forward Expiration [Line Items] |  |
Net Operating Losses | 35 |
2029 [Member] | US [Member] |  |
Schedule Of Tax Credits And Losses Carry Forward Expiration [Line Items] |  |
Net Operating Losses | 9 |
2029 [Member] | Investment tax credits carryforwards [Member] |  |
Schedule Of Tax Credits And Losses Carry Forward Expiration [Line Items] |  |
Investment tax credits | 317 |
2029 [Member] | Non Capital Loss Carryforwards [Member] | CANADA |  |
Schedule Of Tax Credits And Losses Carry Forward Expiration [Line Items] |  |
Non-capital Losses | (9) |
2030 [Member] | UNITED KINGDOM |  |
Schedule Of Tax Credits And Losses Carry Forward Expiration [Line Items] |  |
Net Operating Losses | 21 |
2030 [Member] | US [Member] |  |
Schedule Of Tax Credits And Losses Carry Forward Expiration [Line Items] |  |
Net Operating Losses | 5 |
2030 [Member] | Investment tax credits carryforwards [Member] |  |
Schedule Of Tax Credits And Losses Carry Forward Expiration [Line Items] |  |
Investment tax credits | 346 |
2030 [Member] | Non Capital Loss Carryforwards [Member] | CANADA |  |
Schedule Of Tax Credits And Losses Carry Forward Expiration [Line Items] |  |
Non-capital Losses | 6,288 |
2031 [Member] | UNITED KINGDOM |  |
Schedule Of Tax Credits And Losses Carry Forward Expiration [Line Items] |  |
Net Operating Losses | 37 |
2031 [Member] | US [Member] |  |
Schedule Of Tax Credits And Losses Carry Forward Expiration [Line Items] |  |
Net Operating Losses | 17 |
2031 [Member] | Investment tax credits carryforwards [Member] |  |
Schedule Of Tax Credits And Losses Carry Forward Expiration [Line Items] |  |
Investment tax credits | 486 |
2031 [Member] | Non Capital Loss Carryforwards [Member] | CANADA |  |
Schedule Of Tax Credits And Losses Carry Forward Expiration [Line Items] |  |
Non-capital Losses | 12,121 |
2032 [Member] | UNITED KINGDOM |  |
Schedule Of Tax Credits And Losses Carry Forward Expiration [Line Items] |  |
Net Operating Losses | 43 |
2032 [Member] | US [Member] |  |
Schedule Of Tax Credits And Losses Carry Forward Expiration [Line Items] |  |
Net Operating Losses | 43 |
2032 [Member] | Investment tax credits carryforwards [Member] |  |
Schedule Of Tax Credits And Losses Carry Forward Expiration [Line Items] |  |
Investment tax credits | 363 |
2032 [Member] | Non Capital Loss Carryforwards [Member] | CANADA |  |
Schedule Of Tax Credits And Losses Carry Forward Expiration [Line Items] |  |
Non-capital Losses | 17,278 |
2033 [Member] | UNITED KINGDOM |  |
Schedule Of Tax Credits And Losses Carry Forward Expiration [Line Items] |  |
Net Operating Losses | 56 |
2033 [Member] | US [Member] |  |
Schedule Of Tax Credits And Losses Carry Forward Expiration [Line Items] |  |
Net Operating Losses | 2 |
2033 [Member] | Investment tax credits carryforwards [Member] |  |
Schedule Of Tax Credits And Losses Carry Forward Expiration [Line Items] |  |
Investment tax credits | 193 |
2033 [Member] | Non Capital Loss Carryforwards [Member] | CANADA |  |
Schedule Of Tax Credits And Losses Carry Forward Expiration [Line Items] |  |
Non-capital Losses | 23,240 |
2034 [Member] | UNITED KINGDOM |  |
Schedule Of Tax Credits And Losses Carry Forward Expiration [Line Items] |  |
Net Operating Losses | 48 |
2034 [Member] | US [Member] |  |
Schedule Of Tax Credits And Losses Carry Forward Expiration [Line Items] |  |
Net Operating Losses | 3 |
2034 [Member] | Investment tax credits carryforwards [Member] |  |
Schedule Of Tax Credits And Losses Carry Forward Expiration [Line Items] |  |
Investment tax credits | 215 |
2034 [Member] | Non Capital Loss Carryforwards [Member] | CANADA |  |
Schedule Of Tax Credits And Losses Carry Forward Expiration [Line Items] |  |
Non-capital Losses | 17,077 |
2035 [Member] | UNITED KINGDOM |  |
Schedule Of Tax Credits And Losses Carry Forward Expiration [Line Items] |  |
Net Operating Losses | 28 |
2035 [Member] | US [Member] |  |
Schedule Of Tax Credits And Losses Carry Forward Expiration [Line Items] |  |
Net Operating Losses | 654 |
2035 [Member] | Investment tax credits carryforwards [Member] |  |
Schedule Of Tax Credits And Losses Carry Forward Expiration [Line Items] |  |
Investment tax credits | 122 |
2035 [Member] | Non Capital Loss Carryforwards [Member] | CANADA |  |
Schedule Of Tax Credits And Losses Carry Forward Expiration [Line Items] |  |
Non-capital Losses | 3,112 |
2036 [Member] | UNITED KINGDOM |  |
Schedule Of Tax Credits And Losses Carry Forward Expiration [Line Items] |  |
Net Operating Losses | 3 |
2036 [Member] | US [Member] |  |
Schedule Of Tax Credits And Losses Carry Forward Expiration [Line Items] |  |
Net Operating Losses | 611 |
2036 [Member] | Investment tax credits carryforwards [Member] |  |
Schedule Of Tax Credits And Losses Carry Forward Expiration [Line Items] |  |
Investment tax credits | 79 |
2036 [Member] | Non Capital Loss Carryforwards [Member] | CANADA |  |
Schedule Of Tax Credits And Losses Carry Forward Expiration [Line Items] |  |
Non-capital Losses | 16,664 |
2037 [Member] | UNITED KINGDOM |  |
Schedule Of Tax Credits And Losses Carry Forward Expiration [Line Items] |  |
Net Operating Losses | 578 |
2037 [Member] | US [Member] |  |
Schedule Of Tax Credits And Losses Carry Forward Expiration [Line Items] |  |
Net Operating Losses | 8,530 |
2037 [Member] | Investment tax credits carryforwards [Member] |  |
Schedule Of Tax Credits And Losses Carry Forward Expiration [Line Items] |  |
Investment tax credits | 19 |
2037 [Member] | Non Capital Loss Carryforwards [Member] | CANADA |  |
Schedule Of Tax Credits And Losses Carry Forward Expiration [Line Items] |  |
Non-capital Losses | $ 4,348 |

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