Acquisitions (Details)				1 Months Ended					3 Months Ended								12 Months Ended
	Apr. 29, 2019 USD ($)	Apr. 24, 2019 USD ($)	Oct. 22, 2018 USD ($) customer item	Dec. 31, 2019 USD ($) customer	Nov. 30, 2019 USD ($) customer	Sep. 30, 2019 USD ($) item customer	Dec. 31, 2018 USD ($) item	Jul. 31, 2018 USD ($) customer	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 ($) customer item state	Dec. 31, 2018 USD ($) customer state item	Dec. 31, 2017 USD ($)	Oct. 31, 2018 USD ($)	Oct. 23, 2018 USD ($)
Business Acquisition [Line Items]
Cash paid for acquisitions		$ 900,000,000
Goodwill				$ 63,822,000			$ 52,726,000		$ 63,822,000				$ 52,726,000				$ 63,822,000	$ 52,726,000	$ 42,230,000
Net income									64,227,000	$ 88,489,000	$ 54,903,000	$ 16,924,000	(3,657,000)	$ 78,216,000	$ 66,590,000	$ 50,839,000	224,543,000	191,988,000	239,738,000
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
interest rate swaps settled		$ 83,520,000															83,520,000
2017 Acquisition [Member]
Business Acquisition [Line Items]
Number of acquisitions completed | item																		4
Number of customers | customer																		1,003
Cash paid for acquisitions																		$ 5,860,000
Number of states | state																		2
Goodwill							72,000						72,000					$ 72,000
Operating revenues included in the consolidated financial statements																	$ 878,000	846,000	$ 461,000
Water And Wastewater Utility Systems [Member]
Business Acquisition [Line Items]
Number of acquisitions completed | item																	7
Number of customers | customer																	2,393
Cash paid for acquisitions																	$ 9,437,000
Number of states | state																	3
Operating revenues included in the consolidated financial statements																	$ 506,000
Wastewater Utility System [Member]
Business Acquisition [Line Items]
Number of acquisitions completed | item																	7
Number of customers | customer																	8,661
Total purchase price				42,519,000					42,519,000								$ 42,519,000
Operating revenues																	$ 8,905,000	3,308,000
Delaware County Regional Water Quality Control Authority [Member]
Business Acquisition [Line Items]
Number of municipalities | item																	2
Number of customers | customer																	5,306
Total purchase price				$ 37,000,000					37,000,000								$ 37,000,000
Number of states | state																	2
Interest Rate Swap [Member]
Business Acquisition [Line Items]
Interest rate swap																				$ 850,000
Interest Rate Swap [Member] | LDC Funding LLC [Member]
Business Acquisition [Line Items]
Interest rate swap																					$ 850,000
Pennsylvania [Member] | LDC Funding LLC [Member]
Business Acquisition [Line Items]
Number of acquisitions completed | item			5
Number of customers | customer			747,000
Total purchase price			$ 4,275,000,000
Contingent consideration	$ 120,000,000
Assumed liabilities including debt			1,106,000,000
Decrease in purchase price			1,106,000,000
interest rate swaps settled	$ 83,520,000
Bridge commitment			$ 5,100,000,000
Commitments terminated																	$ 4,350,000,000
Pennsylvania [Member] | Wastewater Utility System [Member]
Business Acquisition [Line Items]
Number of customers | customer				9,887	4,950
Cash paid for acquisitions				$ 50,250,000
Total purchase price					$ 21,000,000		28,338,000						28,338,000					28,338,000
Acquired property, plant and equipment				44,558,000			22,904,000		44,558,000				22,904,000				44,558,000	22,904,000
Goodwill				$ 5,692,000			$ 5,434,000		$ 5,692,000				$ 5,434,000				$ 5,692,000	$ 5,434,000
Number of waste water systems | item							49,000
Operating revenues included in the consolidated financial statements							$ 2,799,000
Pennsylvania [Member] | Delaware County Regional Water Quality Control Authority [Member]
Business Acquisition [Line Items]
Number of municipalities | item						42
Number of customers | customer						16,000
Retail customers | customer						198,000
Total purchase price						$ 276,500,000				$ 276,500,000
Limerick [Member] | Wastewater Utility System [Member]
Business Acquisition [Line Items]
Number of customers | customer								5,497
Total purchase price								$ 74,836,000
Acquired property, plant and equipment								64,759,000
Goodwill								$ 10,790,000