Foreign Currency Transaction Gains and Losses - Summary (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Currency Transaction Gains (Losses) [Line Items]
Net transaction (losses) gains	$ (6,050)	$ 1,613	$ (9,558)	$ (39,505)
Operating (loss) income
Currency Transaction Gains (Losses) [Line Items]
Net transaction (losses) gains	(4,482)	2,857	(9,023)	(32,137)
Other non-operating expense, net
Currency Transaction Gains (Losses) [Line Items]
Net transaction (losses) gains	$ (1,568)	$ (1,244)	$ (535)	$ (7,368)

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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