Segment Information - Additional Segment Information - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Segment Reporting Information [Line Items]
Operating revenues	$ 148,917	$ 134,971	$ 464,863	$ 420,122
Cost of gas	41,193	41,210	153,403	149,748
Environmental remediation	1,509	1,622	5,286	5,627
Operating Segments [Member] \| Natural Gas Distribution [Member]
Segment Reporting Information [Line Items]
Natural Gas Distribution revenues	134,849	122,071	431,402	395,632
Other regulated services	4,765	4,921	9,550	9,847
Operating revenues	139,614	126,992	440,952	405,479
Cost of gas	41,249	41,265	153,515	149,860
Environmental remediation	1,509	1,622	5,286	5,627
Revenue taxes	5,650	4,454	18,305	16,197
NGD margin	$ 91,206	$ 79,651	$ 263,846	$ 233,795

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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