Equity Method Investments - Summarized financial information - Glass Mountain (Details) - Glass Mountain Pipeline LLC [Member] - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Summarized Financial Information, Revenue	$ 6,793	$ 8,348	$ 22,263	$ 29,257
Equity Method Investment, Summarized Financial Information, Cost of Sales	(145)	253	300	2,235
Equity Method Investment, Summarized Financial Information, Operating, General and Administrative Expenses	2,184	1,950	5,647	4,861
Equity Method Investment, Summarized Financial Information, Depreciation and Amortization Expense	3,992	3,903	11,917	11,879
Equity Method Investment, Summarized Financial Information, Net Income (Loss)	$ 761	$ 2,242	$ 4,393	$ 10,278

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://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 323
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=66011266&loc=d3e33918-111571

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 205
-SubTopic 20
-Section 50
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=64827811&loc=SL51721683-107760

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- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 205
-SubTopic 20
-Section 50
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=64827811&loc=SL51721683-107760

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
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-Section 50
-Paragraph 28
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-URI http://asc.fasb.org/extlink&oid=6957238&loc=d3e14064-108612

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 323
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-Section 50
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-URI http://asc.fasb.org/extlink&oid=66011266&loc=d3e33918-111571

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
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-Subparagraph (SX 210.4-08(g))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

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-URI http://asc.fasb.org/extlink&oid=66011266&loc=d3e33912-111571

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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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- 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.

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