Segment Information - Additional Segment Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Segment Reporting Information [Line Items]
Operating revenues	$ 860,400	$ 773,679	$ 746,372
Cost of gas	292,314	262,755	254,911
Environmental remediation	9,938	9,691	12,337
Revenue taxes	34,740	30,291	30,325
Operating Segments [Member] | Natural Gas Distribution [Member]
Segment Reporting Information [Line Items]
NGD operating revenues	797,800	721,950	708,472
Other regulated services	19,087	19,122	12,056
Operating revenues	816,887	741,072	720,528
Cost of gas	292,538	262,980	255,135
Environmental remediation	9,938	9,691	12,337
Revenue taxes	34,600	30,291	30,325
NGD margin	$ 479,811	$ 438,110	$ 422,731