Segment Information - Schedule of Reporting Information (Detail) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2020	Mar. 31, 2019
Segment Reporting Information [Line Items]
Revenues	$ 836,320	$ 833,539	$ 3,122,698	$ 2,959,222
Segment net income (loss)	72,542	94,809	191,669	197,995
Operating Segments
Segment Reporting Information [Line Items]
Revenues	803,118	794,866	2,969,443	2,811,793
Intersegment Eliminations
Segment Reporting Information [Line Items]
Revenues	33,202	38,673	153,255	147,429
Segment Reconciling Items
Segment Reporting Information [Line Items]
Revenues	0	0	0	0
Segment net income (loss)	(853)	(549)	(1,943)	(1,834)
Natural Gas Operations
Segment Reporting Information [Line Items]
Revenues	502,827	520,677	1,351,089	1,384,092
Segment net income (loss)	83,599	103,389	143,381	151,882
Natural Gas Operations | Operating Segments
Segment Reporting Information [Line Items]
Revenues	502,827	520,677	1,351,089	1,384,092
Natural Gas Operations | Intersegment Eliminations
Segment Reporting Information [Line Items]
Revenues	0	0	0	0
Utility Infrastructure Services
Segment Reporting Information [Line Items]
Revenues	333,493	312,862	1,771,609	1,575,130
Segment net income (loss)	(10,204)	(8,031)	50,231	47,947
Utility Infrastructure Services | Operating Segments
Segment Reporting Information [Line Items]
Revenues	300,291	274,189	1,618,354	1,427,701
Utility Infrastructure Services | Intersegment Eliminations
Segment Reporting Information [Line Items]
Revenues	$ 33,202	$ 38,673	$ 153,255	$ 147,429