Foreign Currency Transaction Gains and Losses - Summary (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Currency Transaction Gains (Losses) [Line Items]
Net transaction losses	$ (11,828)	$ (12,985)	$ (3,508)	$ (41,118)
Operating loss
Currency Transaction Gains (Losses) [Line Items]
Net transaction losses	(12,274)	(6,845)	(4,541)	(34,994)
Other non-operating income (expense), net
Currency Transaction Gains (Losses) [Line Items]
Net transaction losses	$ 446	$ (6,140)	$ 1,033	$ (6,124)

Amount before tax of foreign currency transaction realized and unrealized gain (loss) recognized in the income statement.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 830
-SubTopic 20
-Section 50
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-URI http://asc.fasb.org/extlink&oid=6450222&loc=d3e30840-110895

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
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Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 20
-Section 45
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-URI http://asc.fasb.org/extlink&oid=109240200&loc=d3e30690-110894

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