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Debt - E.ON contingent obligation (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2015 USD ($) payment	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Debt Instrument [Line Items]
Unrealized gain (loss) on E.ON obligation	$ 1,411	$ 1,412	$ 16,781
Long-term Debt [Member] | Contingent obligation [Member]
Debt Instrument [Line Items]
Payment terms	72 monthly payments
Stated interest rate	10.94%
Long-term Debt [Member] | E.ON Contingent Obligation [Member]
Debt Instrument [Line Items]
Number of monthly payments | payment	72
Unrealized gain (loss) on E.ON obligation	$ 1,411	1,412
Other Liabilities [Member] | E.ON Contingent Obligation [Member]
Debt Instrument [Line Items]
E.ON contingent obligation – principal	(12,902)	(12,902)
E.ON contingent obligation – accrued interest	(6,702)	(5,291)
E.ON contingent obligation – derivative asset	19,604	18,193
E.ON Contingent Obligation	$ 0	$ 0

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- Definition

Debt Instrument, Payment Terms, Number of Monthly Payments

+ References

No definition available.

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- Definition

This amount represents the accrued interest on the E.ON contingent obligation, which is defined as the sum of the carrying values as of the balance sheet date of the E.ON Contingent Obligation which is debt initially having maturities due after one year from the balance sheet date or beyond the operating cycle, if longer, but excluding the portions thereof scheduled to be repaid within one year or the normal operating cycle, if longer. The E.ON contingent obligation consists of the aggregate E.ON payments. Obligation to make repayments is contingent upon certain operating criteria. When the conditions for repayment are met, and for so long so those conditions continue to be met, there is obligation to make principal and interest payments.

+ References

No definition available.

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- Definition

This amount represents the derivative asset recorded for the E.ON contingent obligation, which is defined as the sum of the carrying values as of the balance sheet date of the E.ON Contingent Obligation which is debt initially having maturities due after one year from the balance sheet date or beyond the operating cycle, if longer, but excluding the portions thereof scheduled to be repaid within one year or the normal operating cycle, if longer. The E.ON contingent obligation consists of the aggregate E.ON payments. Obligation to make repayments is contingent upon certain operating criteria. When the conditions for repayment are met, and for so long so those conditions continue to be met, there is obligation to make principal and interest payments.

+ References

No definition available.

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- Definition

This amount represents the principal amount of the E.ON contingent obligation, which is defined as the sum of the carrying values as of the balance sheet date of the E.ON Contingent Obligation which is debt initially having maturities due after one year from the balance sheet date or beyond the operating cycle, if longer, but excluding the portions thereof scheduled to be repaid within one year or the normal operating cycle, if longer. The E.ON contingent obligation consists of the aggregate E.ON payments. Obligation to make repayments is contingent upon certain operating criteria. When the conditions for repayment are met, and for so long so those conditions continue to be met, there is obligation to make principal and interest payments.

+ References

No definition available.

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- Definition

Sum of the carrying values as of the balance sheet date of the E.ON Contingent Obligation which is debt initially having maturities due after one year from the balance sheet date or beyond the operating cycle, if longer, but excluding the portions thereof scheduled to be repaid within one year or the normal operating cycle, if longer. The E.ON contingent obligation consists of the aggregate E.ON payments. Obligation to make repayments is contingent upon certain operating criteria. When the conditions for repayment are met, and for so long so those conditions continue to be met, there is obligation to make principal and interest payments.

+ References

No definition available.

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- Definition

The net change in the difference between the fair value and the carrying value on the contingent obligation held at each balance sheet date, that was included in earnings for the period.

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No definition available.

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- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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Description of the payment terms of the debt instrument (for example, whether periodic payments include principal and frequency of payments) and discussion about any contingencies associated with the payment.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(3))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 470
-Section 50
-Paragraph 3
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=6479336&loc=d3e64711-112823

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