Segment Information - Additional Segment Information (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2020	Mar. 31, 2019
Segment Reporting Information [Line Items]
Operating revenues	$ 285,151	$ 285,348
Cost of gas	108,538	105,457
Environmental remediation	4,005	8,947
Operating Segments [Member] \| Natural Gas Distribution [Member]
Segment Reporting Information [Line Items]
Natural Gas Distribution revenues	273,561	278,983
Other regulated services	4,926	58
Operating revenues	278,487	279,041
Cost of gas	108,595	105,513
Environmental remediation	4,005	8,947
Revenue taxes	11,743	11,926
NGD margin	$ 154,144	$ 152,655

The charge against earnings in the period for known or estimated future costs arising from requirements to perform environmental remediation activities.

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Amount of operating expense for purchased gas and petroleum of regulated operation.

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