BUSINESS COMBINATIONS - Pro Forma Information (Details) - Elizabethtown Gas and Elkton Gas - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]
Business Acquisition, Pro Forma Revenue	$ 261,203	$ 302,480	$ 1,165,435	$ 1,240,240
Business Acquisition, Pro Forma Net Income (Loss)	$ (34,805)	$ (25,116)	$ 37,433	$ 38,307
Business Acquisition, Pro Forma Earnings Per Share, Basic	$ (0.38)	$ (0.29)	$ 0.41	$ 0.46

The pro forma basic net income per share for a period as if the business combination or combinations had been completed at the beginning of a period.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
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The pro forma net Income or Loss for the period as if the business combination or combinations had been completed at the beginning of a period.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
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The pro forma revenue for a period as if the business combination or combinations had been completed at the beginning of the period.

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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
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-URI http://asc.fasb.org/extlink&oid=79982066&loc=d3e1392-128463

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