Derivatives and Hedging - Outstanding Derivatives Contracts (Details) $ in Thousands	6 Months Ended	12 Months Ended
Jun. 30, 2018 USD ($) outstanding_contract	Dec. 31, 2017 USD ($) outstanding_contract
Derivatives, Fair Value [Line Items]
Number of Outstanding Contracts \| outstanding_contract	49	142
Notional Amounts	$ 1,743,666	$ 2,086,764
Fair Value Asset (Liability), Net	21,979	3,860
Unrealized Gain Recorded in AOCI/L	$ 16,281	$ 2,483
Designated as hedging instrument \| Other assets \| Interest rate swaps
Derivatives, Fair Value [Line Items]
Number of Outstanding Contracts \| outstanding_contract	5	5
Notional Amounts	$ 1,400,000	$ 1,400,000
Fair Value Asset (Liability), Net	22,380	3,412
Unrealized Gain Recorded in AOCI/L	$ 16,281	$ 2,483
Not Designated as Hedging Instrument \| Accrued liabilities \| Foreign currency forwards
Derivatives, Fair Value [Line Items]
Number of Outstanding Contracts \| outstanding_contract	44
Notional Amounts	$ 343,666
Fair Value Asset (Liability), Net	(401)
Unrealized Gain Recorded in AOCI/L	$ 0
Not Designated as Hedging Instrument \| Other current assets \| Foreign currency forwards
Derivatives, Fair Value [Line Items]
Number of Outstanding Contracts \| outstanding_contract		137
Notional Amounts		$ 686,764
Fair Value Asset (Liability), Net		448
Unrealized Gain Recorded in AOCI/L		$ 0

Aggregate notional amount specified by the derivative(s). Expressed as an absolute value.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 12
-Section 13
-Sentence Column B

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Fair values as of the balance sheet date of the net amount of all assets and liabilities resulting from contracts that meet the criteria of being accounted for as derivative instruments.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 45
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41228-113958

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- Definition

The number of derivative instruments of a particular group held by the entity.

+ References

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-Name Accounting Standards Codification
-Topic 815
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-Section 50
-Paragraph 1A
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Amount before tax of increase (decrease) in accumulated gain (loss) from derivative instruments designated and qualifying as the effective portion of cash flow hedges and an entity's share of an equity investee's increase (decrease) in deferred hedging gain (loss).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 11
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