Amount of increase (decrease) in the fair value of derivatives recognized in the income statement.

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
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Amount of increase in the fair value of derivatives recognized in the income statement.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4C
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Amount of decrease in the fair value of derivatives recognized in the income statement.

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The net change in the difference between the fair value and the carrying value, or in the comparative fair values, of derivative instruments, including options, swaps, futures, and forward contracts, held at each balance sheet date, that was included in earnings for the period.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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-Topic 230
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-Section 45
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Derivative Instruments - Realized and unrealized gains and (losses) on derivative instruments (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Gains and (losses) on derivative instruments
Net unrealized losses on derivative instruments			$ (14,961)		$ (6,328)
Natural gas swaps \| Regulatory asset
Gains and (losses) on derivative instruments
Net unrealized losses on derivative instruments			(14,961)		$ (6,328)
Natural gas swaps \| Fuel
Gains and (losses) on derivative instruments
Gains	$ 863	$ 778	2,614	$ 3,514
Losses	(97)	(678)	(956)	(1,495)
Total	$ 766	$ 100	$ 1,658	$ 2,019