Foreign Currency Transaction Gains and Losses - Summary (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2018	Mar. 31, 2017
Currency Transaction Gains (Losses) [Line Items]
Net transaction gains (losses)	$ 8,318	$ (28,133)
Operating income (loss)
Currency Transaction Gains (Losses) [Line Items]
Net transaction gains (losses)	7,731	(28,149)
Other non-operating expense, net
Currency Transaction Gains (Losses) [Line Items]
Net transaction gains (losses)	$ 587	$ 16

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

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 830
-SubTopic 20
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6450222&loc=d3e30840-110895

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 830
-SubTopic 20
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=64836518&loc=d3e30700-110894

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 830
-SubTopic 20
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=64836518&loc=d3e30690-110894

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