Segment Information - Schedule of Reporting Information (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Jun. 30, 2020	Sep. 30, 2019	Jun. 30, 2019
Segment Reporting Information [Line Items]
Revenues	$ 791,226	$ 725,230	$ 2,384,793	$ 2,271,780		$ 3,232,930		$ 3,058,434
Segment net income (loss)	18,273	5,353	128,780	122,218	$ 220,498	220,498	$ 191,522	191,522
Operating Segments
Segment Reporting Information [Line Items]
Revenues	759,134	690,876	2,282,576	2,149,671		3,094,096		2,897,089
Segment Reconciling Items
Segment Reporting Information [Line Items]
Revenues	(32,092)	(34,354)	(102,217)	(122,109)		(138,834)		(161,345)
Segment net income (loss)	(627)	(473)	(1,724)	(1,253)		(2,110)		(1,433)
Natural Gas Operations
Segment Reporting Information [Line Items]
Revenues	210,834	209,980	976,095	989,368		1,355,666		1,359,581
Segment net income (loss)	(15,973)	(20,012)	79,568	86,746		155,993		146,287
Natural Gas Operations | Operating Segments
Segment Reporting Information [Line Items]
Revenues	210,834	209,980	976,095	989,368		1,355,666		1,359,581
Natural Gas Operations | Segment Reconciling Items
Segment Reporting Information [Line Items]
Revenues	0	0	0	0		0		0
Utility Infrastructure Services
Segment Reporting Information [Line Items]
Revenues	580,392	515,250	1,408,698	1,282,412		1,877,264		1,698,853
Segment net income (loss)	34,873	25,838	50,936	36,725		66,615		46,668
Utility Infrastructure Services | Operating Segments
Segment Reporting Information [Line Items]
Revenues	548,300	480,896	1,306,481	1,160,303		1,738,430		1,537,508
Utility Infrastructure Services | Segment Reconciling Items
Segment Reporting Information [Line Items]
Revenues	$ (32,092)	$ (34,354)	$ (102,217)	$ (122,109)		$ (138,834)		$ (161,345)