ACQUISITION (Details) - Talen's Wholesale Natural Gas Energy Contracts - USD ($) $ in Thousands		12 Months Ended
Jul. 27, 2017	Sep. 30, 2017
Business Acquisition [Line Items]
Total purchase price consideration transferred	$ 55,661
Net assets acquired	55,661
Goodwill		$ 0
Acquisition related transaction costs		300
Revenue attributable to the acquisition		20,500
Operating loss attributable to the acquisition		281
Wholesale Energy Contracts
Business Acquisition [Line Items]
Wholesale energy contracts	41,846
Amortization expense		$ 762
Retail Energy Contracts
Business Acquisition [Line Items]
Retail energy contracts	$ 13,815
Minimum \| Wholesale Energy Contracts
Business Acquisition [Line Items]
Useful life	1 year
Minimum \| Retail Energy Contracts
Business Acquisition [Line Items]
Useful life	0 years
Maximum \| Wholesale Energy Contracts
Business Acquisition [Line Items]
Useful life	9 years
Maximum \| Retail Energy Contracts
Business Acquisition [Line Items]
Useful life	4 years

Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Derivative Assets

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- Definition

The aggregate expense charged against earnings to allocate the cost of intangible assets (nonphysical assets not used in production) in a systematic and rational manner to the periods expected to benefit from such assets. As a noncash expense, this element is added back to net income when calculating cash provided by or used in operations using the indirect method.

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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.

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No definition available.

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- Definition

This element represents acquisition-related costs incurred to effect a business combination which costs have been expensed during the period. Such costs include finder's fees; advisory, legal, accounting, valuation, and other professional or consulting fees; general administrative costs, including the costs of maintaining an internal acquisitions department; and may include costs of registering and issuing debt and equity securities.

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- Definition

Amount of consideration transferred, consisting of acquisition-date fair value of assets transferred by the acquirer, liabilities incurred by the acquirer, and equity interest issued by the acquirer.

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- Definition

This element represents the amount of earnings or loss of the acquiree since the acquisition date included in the consolidated income statement for the reporting period.

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- Definition

This element represents the amount of revenue of the acquiree since the acquisition date included in the consolidated income statement for the reporting period.

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The amount of identifiable intangible assets recognized as of the acquisition date.

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- Definition

Amount recognized as of the acquisition date for the identifiable assets acquired in excess of (less than) the aggregate liabilities assumed.

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- Definition

Useful life of finite-lived intangible assets, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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No definition available.

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- Definition

Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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