Consolidated Statements Of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Cash flows from operating activities:
Net income	$ 224,543	$ 191,988	$ 239,738
Adjustments to reconcile net income to net cash flows from operating activities:
Depreciation and amortization	156,476	146,673	136,724
Deferred income taxes	(10,436)	(14,950)	13,780
Provision for doubtful accounts	5,306	5,305	4,986
Stock-based compensation	7,368	7,567	6,342
(Gain) loss on sale of utility system and market-based business unit	(405)		774
Loss on interest rate swap agreements	23,742	59,779
Loss on debt extinguishment	18,528
Settlement of interest rate swap agreements	(83,520)
Gain on sale of other assets	(923)	(714)	(484)
Net change in receivables, inventory and prepayments	(4,335)	(18,024)	(6,458)
Net change in payables, accrued interest, accrued taxes and other accrued liabilities	5,108	567	(763)
Pension and other postretirement benefits contributions	(8,597)	(14,216)	(16,240)
Other	5,668	4,547	2,919
Net cash flows from operating activities	338,523	368,522	381,318
Cash flows from investing activities:
Property, plant and equipment additions, including the debt component of allowance for funds used during construction of $4,231, $3,332, and $3,578	(550,273)	(495,737)	(478,089)
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)
Cash flows from financing activities:
Customers' advances and contributions in aid of construction	9,092	7,458	7,312
Repayments of customers' advances	(6,825)	(6,217)	(6,536)
Net proceeds (repayments) of short-term debt	10,275	11,799	(2,885)
Proceeds from long-term debt	1,434,506	1,331,868	591,024
Repayments of long-term debt	(1,048,471)	(914,125)	(359,068)
Extinguishment of long-term debt	(25,237)
Change in cash overdraft position	1,993	(12,678)	9,012
Proceeds from issuance of common stock under dividend reinvestment plan	8,959	5,163	1,453
Proceeds from stock issued to finance acquisition	1,263,099
Proceeds from tangible 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
Cash paid during the year for:
Interest, net of amounts capitalized	89,228	93,630	81,771
Income taxes	970	2,103	3,177
Non-cash investing activities:
Property, plant and equipment additions purchased at the period end, but not yet paid	60,628	65,285	45,385
Non-cash utility property contributions	$ 30,693	$ 24,660	$ 39,220