Consolidated Statements Of Cash Flow - USD ($) $ in Thousands	3 Months Ended				9 Months Ended		12 Months Ended
	Sep. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Cash flows from operating activities:
Net income	$ 55,732	$ 51,781	$ 88,489	$ 16,924	$ 182,142	$ 160,316
Adjustments to reconcile net income to net cash flows from operating activities:
Depreciation and amortization					186,078	115,973
Deferred income taxes					1,120	(10,359)
Provision for doubtful accounts					23,598	3,622
Stock-based compensation					5,842	5,831
Gain on sale of other assets	(233)		(175)		(358)	(443)
Loss (gain) on sale of utility system					19	(403)
Loss on interest rate swap agreements						23,742
Loss on debt extinguishment						18,920
Settlement of interest rate swap agreements						(83,520)
Net change in receivables, inventory and prepayments					24,886	(11,657)
Net change in payables, accrued interest, accrued taxes and other accrued liabilities					12,431	13,324
Pension and other postretirement benefits contributions					(16,100)	(8,579)
Other					997	1,262
Net cash flows from operating activities					420,655	228,029
Cash flows from investing activities:
Property, plant and equipment additions, including the debt component of allowance for funds used during construction of $2,957 and $3,253					(554,141)	(401,558)
Acquisitions of utility systems, net					(3,467,032)	(619)
Net proceeds from the sale of other assets					1,063	2,361
Other					465	2,296
Net cash flows used in investing activities					(4,019,645)	(397,520)
Cash flows from financing activities:
Customers' advances and contributions in aid of construction					7,475	8,692
Repayments of customers' advances					(3,992)	(2,245)
Net repayments of short-term debt					(160,420)	(5,449)
Proceeds from long-term debt					2,957,663	1,310,061
Repayments of long-term debt					(1,647,354)	(888,951)
Extinguishment of long-term debt						(25,237)
Change in cash overdraft position					18,166	(3,882)
Issuance of common stock under dividend reinvestment plan					12,322	4,819
Issuance of common stock from private placement					729,301
Proceeds from stock issued to finance acquisition						1,263,099
Proceeds from tangible equity unit issuance						673,642
Proceeds from exercised stock options					1,215	1,735
Repurchase of common stock					(4,345)	(1,867)
Dividends paid on common stock					(171,079)	(136,821)
Other					(390)	(1,164)
Net cash flows from financing activities					1,738,562	2,196,432
Net change in cash and cash equivalents					(1,860,428)	2,026,941
Cash and cash equivalents at beginning of period		$ 1,868,922		$ 3,627	1,868,922	3,627	$ 3,627
Cash and cash equivalents at end of period	$ 8,494		$ 2,030,568		8,494	2,030,568	$ 1,868,922
Non-cash investing activities:
Property, plant and equipment additions purchased at the period end, but not yet paid for					96,982	41,059
Non-cash customer advances and contributions in aid of construction					$ 28,321	$ 24,633