Summary of Significant Accounting Policies (Revenue) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Accounting Policies [Abstract]
Revenue from contracts with customers	$ 447,720	$ 389,302	$ 381,777
Alternative revenue programs, net	(18,232)	10,456	12,584
Other balancing and memorandum accounts revenue, net	(14,403)	(7,541)	(10,838)
Rental income	5,397	5,482	5,702
Operating revenue	420,482	397,699	389,225
Balancing and Memorandum Cost Recovery Account, Increase (Decrease)	962	2,643
Regulated operating revenue, water surcharge	$ 4,955	$ 5,013	$ 5,017