Schedule 1 - Condensed Parent Company Financial Statements (Condensed Statements of Cash Flows) (Details) - USD ($) $ in Thousands		1 Months Ended	12 Months Ended
	May 18, 2019	May 31, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Condensed Cash Flow Statements, Captions [Line Items]
Net cash flows from operating activities			$ 338,523	$ 368,522	$ 381,318
Acquisitions of utility systems and other, net			(59,687)	(145,693)	(5,860)
Net proceeds from the sale of utility systems and other assets			2,893	716	1,342
Other			2,464	899	2,223
Net cash flows used in investing activities			(604,603)	(639,815)	(480,384)
Proceeds from long-term debt			1,434,506	1,331,868	591,024
Repayments of long-term debt		$ (313,500)	(1,048,471)	(914,125)	(359,068)
Extinguishment of long-term debt	$ (25,237)	$ (25,237)	(25,237)
Proceeds from stock issued to finance pending acquisition			1,263,099
Proceeds from equity unit issuance			673,642
Proceeds from exercised stock options			1,898	1,459	2,873
Repurchase of common stock			(1,867)	(2,555)	(2,167)
Dividends paid on common stock			(188,512)	(150,736)	(140,660)
Other			(1,177)	(720)	(851)
Net cash flows from financing activities			2,131,375	270,716	99,507
Net increase (decrease) in cash and cash equivalents			1,865,295	(577)	441
Cash and cash equivalents at beginning of year			3,627	4,204	3,763
Cash and cash equivalents at end of year			1,868,922	3,627	4,204
Parent Company [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Net cash flows from operating activities			(54,496)	(12,930)	98,821
Acquisitions of utility systems and other, net			(6,385)	(103,364)	(220)
Decrease (increase) in investment of subsidiary			6,068	(13,258)	20,021
Other			235	241	1,811
Net cash flows used in investing activities			(82)	(116,381)	21,612
Proceeds from long-term debt			1,009,992	1,107,600	286,969
Repayments of long-term debt			(821,226)	(830,900)	(268,050)
Extinguishment of long-term debt			(25,237)
Proceeds from stock issued to finance pending acquisition			1,263,099
Proceeds from equity unit issuance			673,642
Proceeds from issuing common stock			8,959	5,163	1,453
Proceeds from exercised stock options			1,898	1,459	2,873
Repurchase of common stock			(1,867)	(2,555)	(2,167)
Dividends paid on common stock			(188,512)	(150,736)	(140,660)
Other			(1,177)	(720)	(851)
Net cash flows from financing activities			1,919,571	129,311	(120,433)
Net increase (decrease) in cash and cash equivalents			1,864,993
Cash and cash equivalents at beginning of year
Cash and cash equivalents at end of year			$ 1,864,993