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Business Combination (Details) $ / shares in Units, $ in Thousands |  |  | 3 Months Ended |
--- | --- | --- | --- | ---
Oct. 09, 2019 USD ($) $ / shares | Oct. 08, 2019 USD ($) | Mar. 31, 2020 USD ($) people_served connection municipality | Mar. 31, 2019 USD ($) shares | Dec. 31, 2019 USD ($)
Business Acquisition [Line Items] |  |  |  |  |
Long-term borrowings |  |  | $ 35,000 | $ 80,000 |
Borrowings on line of credit |  |  | 47,424 | $ 38,000 |
Assets Acquired |  |  |  |  |
Goodwill |  |  | 628,287 |  | $ 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 |  |  | 626,523 |  |
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets |  |  | 1,536,141 |  |
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 |  |  | 125,772 |  |
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 |  |  | 694,293 |  |
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 |  |

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