Summary Of Significant Accounting Policies (Narrative) (Details)	3 Months Ended								12 Months Ended
	Dec. 31, 2019 USD ($)	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2019 USD ($) segment county state	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Jan. 01, 2019 USD ($)
Summary Of Significant Accounting Policies [Line Items]
Percentage of operating revenue from largest operating subsidiary									54.00%
Percentage of net income from largest operating subsidiary									72.00%
Number of operating segments | segment									10
Number of reportable segments | segment									1
Operating revenues	$ 226,042,000	$ 243,626,000	$ 218,892,000	$ 201,132,000	$ 205,747,000	$ 226,137,000	$ 211,860,000	$ 194,347,000	$ 889,692,000	$ 838,091,000	$ 809,525,000
Net utility plant acquisition adjustment	15,248,000								15,248,000
Amortization of the acquisition adjustments									6,076,000	2,645,000	2,774,000
Utility expenditures expected to be recovered	1,360,000								1,360,000
Deferred cost reported as a component of net property, plant and equipment	16,680,000								16,680,000
Amount of AFUDC related to equity funds	11,941,000				9,691,000				11,941,000	9,691,000	11,633,000
Capitalized interest									0
Overdraft for certain disbursement cash accounts	$ 10,944,000				$ 8,950,000				$ 10,944,000	8,950,000
Amortization period of tax repair catch up adjustment									10 years
Impaired goodwill									$ 0
Adjustments for New Accounting Principle, Early Adoption [Member]
Summary Of Significant Accounting Policies [Line Items]
Assets and lease liability												$ 14,028,000
Joint Venture [Member]
Summary Of Significant Accounting Policies [Line Items]
Joint venture ownership percentage	49.00%								49.00%
Joint Venture Distributions									$ 3,185,000	1,793,000
Pennsylvania [Member]
Summary Of Significant Accounting Policies [Line Items]
Number of counties providing operating services | county									27
Other State [Member]
Summary Of Significant Accounting Policies [Line Items]
Number of states providing services in other than Pennsylvania | state									7
Minimum [Member]
Summary Of Significant Accounting Policies [Line Items]
Amortized Period									2 years
Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Amortized Period									59 years
Regulated [Member]
Summary Of Significant Accounting Policies [Line Items]
Number of operating segments | segment									8
Operating revenues									$ 886,430,000	834,638,000	804,905,000
Unregulated Operation [Member]
Summary Of Significant Accounting Policies [Line Items]
Operating revenues									$ 3,395,000	$ 3,590,000	$ 4,798,000