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Income taxes - Changes in Valuation Allowance (Details) - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Movement in Valuation Allowances and Reserves [Roll Forward] |  |  |
Balance, valuation allowance | $ 839,082 | $ 768,764 | $ 748,283
Remeasurement of deferred tax assets | (205,150) | 0 | 0
Release of valuation allowance | 0 | (6,007) | 0
Other change in valuation allowance | (26,119) | 76,325 | 20,481
Balance, valuation allowance | $ 607,813 | $ 839,082 | $ 768,764

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- Definition Valuation Allowance, Deferred Tax Asset, Release of Valuation Allowance + References No definition available. + Details
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- Definition Valuation Allowance, Deferred Tax Asset, Remeasurement Due To Tax Cuts & Jobs Act + References No definition available. + Details
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- Definition A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period. + References No definition available. + Details
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- Definition Amount of increase (decrease) in the valuation allowance for a specified deferred tax asset. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 45 -Paragraph 20 -URI http://asc.fasb.org/extlink&oid=84176650&loc=d3e32123-109318 + Details
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- Definition Total of allowances and reserves, the valuation and qualifying accounts that are either netted against the cost of an asset (in order to value it at its carrying value) or that reflect a liability established to represent expected future costs. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section S99 -Paragraph 4 -Subparagraph (SX 210.12-09) -URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e24092-122690 + Details
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