Business Combination (Details) $ / shares in Units, $ in Thousands			6 Months Ended
	Oct. 09, 2019 USD ($) $ / shares	Oct. 08, 2019 USD ($)	Jun. 30, 2020 USD ($) connection people_served municipality	Jun. 30, 2019 USD ($) shares	Dec. 31, 2019 USD ($)
Business Acquisition [Line Items]
Long-term borrowings			$ 35,000	$ 80,000
Borrowings on line of credit			89,196	$ 66,000
Assets Acquired
Goodwill			628,343		$ 628,287
CTWS [Member]
Business Acquisition [Line Items]
Business Combination, Consideration Transferred, Acquiree's Common Shares Converted In Cash Per Share | $ / shares	$ 70.00
Payments to Acquire Businesses, Gross	$ 838,476
Cash Acquired from Acquisition	3,011
Adjustments to Additional Paid in Capital, Share-based Compensation, Equity Award Assumed in Acquisition	6,384
Long-term borrowings	18,463
Borrowings on line of credit	$ 60,000
Assets Acquired
Utility plant, net			750,703
Nonutility plant			848
Current assets			42,673
Investments			12,489
Regulatory assets and deferred charges, less current portion			83,132
Other intangible assets			17,181
Other assets			2,592
Goodwill			626,548
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets			1,536,166
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Liabilities [Abstract]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities, Long-term Debt			281,009
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities			125,797
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Deferred Tax Liabilities			107,789
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Post-retirement Benefit Plans			31,789
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, CIAC and Advances			137,327
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities			10,607
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Liabilities			694,318
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net			$ 841,848
Connecticut Water Service, Inc. [Member]
Business Acquisition [Line Items]
Public Utilities, Service Connections | connection			138,000
Public Utilities, Number of People Served | people_served			480,000
Public Utilities, Number of Communities Served | municipality			80
Underwritten Public Offering [Member] | Common Stock
Business Acquisition [Line Items]
Stock Issued During Period, Shares, New Issues | shares				7,762,000
Proceeds from Issuance of Common Stock, Gross				$ 411,077
Series 2019A/B/C [Member] | Senior Notes [Member] | Parent Company [Member]
Business Acquisition [Line Items]
Principal Debt Sold		$ 427,398
Southbury, Connecticut [Member] | Connecticut Water Service, Inc. [Member]
Business Acquisition [Line Items]
Public Utilities, Service Connections | connection			3,000