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Quarterly information (Unaudited) - 2014 Financial Results Overview (Details) - USD ($) $ in Thousands	3 Months Ended					12 Months Ended
	Dec. 31, 2015	Mar. 31, 2015	Dec. 31, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Quarterly Financial Data [Abstract]
Unrealized gain on fair value of contingent consideration		$ 6,527	$ 7,943			$ 18,337	$ 7,943	$ 0
Gain on remeasurement of equity investment			15,955			0	15,955	0
Pension charges	$ 3,400		4,964
Litigation settlement expense			$ 2,616	$ 500
Sebree power contract amortization					$ 5,534	$ 0	$ 5,534	$ 31,031
Increase (decrease) in litigation reserve					$ (3,100)

X

- Definition

The aggregate benefit recognized in earnings to allocate the assumed power contract liability in a systematic and rational manner over the contract period. As a noncash benefit, this element is subtracted from net income when calculating cash provided by or used in operations using the indirect method.

+ References

No definition available.

+ Details

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X

- Definition

The revenues and gains recognized recorded for each transaction with the acquiree that is recognized separately from the acquisition of assets and assumptions of liabilities in the business combination.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (e)(3)
-URI http://asc.fasb.org/extlink&oid=56956515&loc=d3e1392-128463

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X

- Definition

In a business combination achieved in stages, this element represents the amount of gain recognized by the entity as a result of remeasuring to fair value the equity interest in the acquiree it held before the business combination.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (g)(2)
-URI http://asc.fasb.org/extlink&oid=56956515&loc=d3e1392-128463

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X

- Definition

Amount of net gain (loss) recognized in net periodic benefit cost due to settlements and curtailments. Curtailments result from an event that significantly reduces the expected years of future service of present employees or eliminates for a significant number of employees the accrual of defined benefits for some or all of their future services. Settlements result from an irrevocable action that relieves the employer (or the plan) of primary responsibility for a benefit obligation and eliminates significant risks related to the obligation and the assets used to effect the settlement. Examples of transactions that constitute a settlement include, but are not limited to, lump-sum cash payments to plan participants in exchange for their rights to receive specified benefits and purchasing nonparticipating annuity contracts to cover vested benefits.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (h)(7)
-URI http://asc.fasb.org/extlink&oid=58740216&loc=d3e1928-114920

+ Details

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Data Type:	xbrli:monetaryItemType
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X

- Definition

Amount of increase (decrease) in liability to reflect the estimated ultimate cost of settling claims relating to insured events that have occurred on or before the balance sheet date, whether or not reported to the insurer at that date.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=56944662&loc=d3e3602-108585

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

X

- Definition

Amount of litigation expense, including but not limited to legal, forensic, accounting, and investigative fees.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

X

- References

No definition available.

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