Summary of Significant Accounting Policies (Regulatory Rate Filings) (Details) - USD ($)										1 Months Ended	11 Months Ended	12 Months Ended
	Feb. 06, 2018	Nov. 29, 2017	Nov. 15, 2017	Jun. 26, 2017	Jun. 01, 2017	Apr. 03, 2017	Feb. 17, 2017	Nov. 15, 2016	Dec. 03, 2015	Jun. 30, 2016	Nov. 28, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Jan. 04, 2018	Sep. 27, 2017	Jun. 06, 2017
Public Utilities General Disclosures [Line Items]
Balancing Account, Revenue Increase (Reduction)												$ 3,137,000	$ 11,024,000	$ 2,745,000
Authorized Regulatory Surcharge, Per 15 CCF							$ 1.52
Public Utilities, Requested Rate Increase (Decrease), Amount						$ 7,550,000	$ 5,339,000	$ 13,205,000
Public Utilities, Requested Rate Increase (Decrease), Percentage						2.10%	1.50%	3.80%
Water Reduction Target Goal, Percentage										20.00%
Public Utilities, Approved Rate Increase (Decrease), Percentage			4.22%	3.46%
Requested Service Charge Refund																	$ 1,794,000
Public Utilities, Approved Reimbursement Fee, Percentage		1.40%									1.44%
Public Utilities, Approved Rate Increase (Decrease), Amount			$ 15,670,000	$ 12,407,000
Balancing and Memorandum Account, Surcharge Offset												1,035,000	0	0
Regulatory Balancing and Memorandum Accounts, Net Under-Collected												$ 3,738,000				$ 11,474,000
Regulatory Balancing and Memorandum Accounts Review, Authorized Revenue, Threshold Percentage												2.00%
Regulatory Assets and Liabilities [Abstract]
Net Regulatory Assets												$ 99,554,000	151,773,000
Current regulatory assets, net												0	16,064,000
Total regulatory assets, net, less current portion												99,554,000	135,709,000
Public Utilities, Requested Return on Equity, Percentage						9.43%
Public Utilities, Requested Equity Capital Structure, Percentage						8.09%
Regulatory Liabilities												62,476,000	0
Deferred Income Tax Charge
Regulatory Assets and Liabilities [Abstract]
Regulatory assets												0	10,139,000
Postretirement pensions and other medical benefits [Member]
Regulatory Assets and Liabilities [Abstract]
Regulatory assets												68,556,000	109,795,000
Balancing and Memorandum Accounts [Member]
Regulatory Assets and Liabilities [Abstract]
Regulatory assets												27,925,000	25,909,000
Other Regulatory Assets [Member]
Public Utilities General Disclosures [Line Items]
Balancing Account, Revenue Increase (Reduction)												(678,000)	(483,000)	(293,000)
Regulatory Assets and Liabilities [Abstract]
Regulatory assets												3,073,000	5,930,000
2014 WCMA [Member]
Public Utilities General Disclosures [Line Items]
Memorandum Account, Authorized Recovery					$ 996,000				$ 4,259,000
Authorized Regulatory Surcharge, Per CCF					0.08				$ 0.08
WCMA Reserve												0	1,090,000	1,278,000
2015 WCMA [Member]
Public Utilities General Disclosures [Line Items]
Memorandum Account, Authorized Recovery					2,233,000									19,854,000
Authorized Regulatory Surcharge, Per CCF					$ 0.1441
WCMA Reserve												0	2,115,000	2,343,000
Balancing and Memorandum Account, Surcharge Offset														12,139,000
Authorized Regulatory Surcharge, Net														$ 5,372,000
Subsequent Event [Member]
Public Utilities General Disclosures [Line Items]
Requested rate increase for 2016															$ 34,288,000
Requested rate increase for 2016 as percentage of total revenue at time of request															9.76%
Requested rate increase for 2017															$ 14,232,000
Requested rate increase for 2017 as percentage of total revenue at time of request															3.70%
Requested rate increase for 2018															$ 20,582,000
Requested rate increase for 2018 as percentage of total revenue at time of request															5.17%
Memorandum Account, Authorized Recovery															$ 20,725,000
Regulatory Assets and Liabilities [Abstract]
Public Utilities, Proposed Return on Equity, Percentage	8.30%
Public Utilities, Proposed Equity Capital Structure, Percentage	7.19%
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount	$ (10,000,000)
Deferred Income Tax Charge
Regulatory Assets and Liabilities [Abstract]
Regulatory Liabilities												$ 62,476,000	$ 0