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Long-term investments - Narrative (Details) - USD ($) $ in Thousands |  | 12 Months Ended
--- | --- | ---
Jan. 01, 2018 | Dec. 31, 2018 | Dec. 31, 2017
Investment [Line Items] |  |  |
Accumulated other comprehensive loss |  | $ 146,153 | $ 94,294
Deferred tax expense (income) |  | 38,392 | (20,170)
Deficit |  | (547,839) | (610,908)
Unrealized gain (loss) on investments, net of deferred tax expense |  | $ (6,221) | $ 1,141
Increase (decrease) due to changes in accounting policy required by IFRSs | IFRS 9 |  |  |
Investment [Line Items] |  |  |
Accumulated other comprehensive loss | $ 46,000 |  |
Deficit | 46,000 |  |
Increase (decrease) due to changes in accounting policy required by IFRSs | Long Term Investments | IFRS 9 |  |  |
Investment [Line Items] |  |  |
Accumulated other comprehensive loss | 35,000 |  |
Deferred tax expense (income) | (1,000) |  |
Deficit | $ 35,000 |  |

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