Equity Method Investments - Summarized financial information - White Cliffs (Details) - White Cliffs Pipeline, L.L.C. [Member] - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Summarized income statement information
Equity Method Investment, Summarized Financial Information, Revenue	$ 43,855	$ 45,445	$ 128,455	$ 145,288
Equity Method Investment, Summarized Financial Information, Cost of Sales	(107)	(360)	(138)	8,091
Equity Method Investment, Summarized Financial Information, Operating, General and Administrative Expenses	5,514	5,723	17,511	17,849
Equity Method Investment, Summarized Financial Information, Depreciation and Amortization Expense	9,624	9,154	28,821	27,619
Equity Method Investment, Summarized Financial Information, Net Income (Loss)	$ 28,825	$ 30,928	$ 82,262	$ 91,688

Equity method investment, summarized financial information, depreciation and amortization expense.

No definition available.

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- Definition

Equity method investment, summarized financial information, operating, general and administrative expenses.

+ References

No definition available.

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- Definition

The amount of the cost of sales reported by an equity method investment of the entity.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 205
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- References

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- Definition

The amount of net income (loss) reported by an equity method investment of the entity.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 323
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-Publisher FASB
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- Definition

The amount of revenue from sale of goods and services reduced by sales returns, allowances, and discounts reported by an equity method investment of the entity.

+ References

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