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

+ Details

Name:	invest_DerivativeNotionalAmount
Namespace Prefix:	invest_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	instant

- Definition

Amount of contractual obligation due in the next fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

No definition available.

+ Details

Name:	us-gaap_ContractualObligationDueInNextTwelveMonths
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of contractual obligation due in the second fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

No definition available.

+ Details

Name:	us-gaap_ContractualObligationDueInSecondYear
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Average contractual rate at which a foreign currency can be purchased or sold.

+ References

No definition available.

+ Details

Name:	us-gaap_DerivativeAverageForwardExchangeRate1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_DerivativeLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Fair value as of the balance sheet date of all foreign currency derivatives not designated as hedging instruments.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-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

+ Details

Name:	us-gaap_ForeignCurrencyDerivativeInstrumentsNotDesignatedAsHedgingInstrumentsAtFairValueNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=us-gaap_ForeignExchangeForwardMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CurrencyAxis=currency_NOK
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CurrencyAxis=currency_EUR
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Derivative Instruments - Foreign Currency Forward Contracts (Details) $ in Thousands	Dec. 31, 2018 USD ($)	Dec. 31, 2018 NOK (kr)	Dec. 31, 2018 EUR (€)
Foreign currency forward contracts
Derivative [Line Items]
Fair Value / Carrying Amount of Asset/(Liability) Non-hedge	$ (4,650)
Expected Maturity - 2019	61,786
Expected Maturity - 2020	$ 5,567
Norwegian Krone
Derivative [Line Items]
Notional amount \| kr		kr 425,000,000
Average Forward Rate	7.96	7.96	7.96
Norwegian Krone \| Foreign currency forward contracts
Derivative [Line Items]
Fair Value / Carrying Amount of Asset/(Liability) Non-hedge	$ (4,588)
Expected Maturity - 2019	47,809
Expected Maturity - 2020	$ 5,567
Euro
Derivative [Line Items]
Notional amount \| €			€ 12,000,000
Average Forward Rate	0.86	0.86	0.86
Euro \| Foreign currency forward contracts
Derivative [Line Items]
Fair Value / Carrying Amount of Asset/(Liability) Non-hedge	$ (62)
Expected Maturity - 2019	13,977
Expected Maturity - 2020	$ 0