Summary of Significant Accounting Policies (Advances for Construction and Contributions in Aid of Construction) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Accounting Policies [Abstract]
Refund period for advances for construction received after 1981	40 years
Estimated Refunds of Advances for Construction [Abstract]
2020	$ 2,890
2021	2,890
2022	2,890
2023	2,878
2024	2,799
Thereafter	49,631
Customer Advances for Construction	112,339	$ 80,610
Customer Advances for Construction, Non-Refundable	21,463
Customer Advances for Construction, Refunded on Service Connections	$ 26,898
Amortization period for taxes paid relating to advances and contributions	40 years