Organization, Summary of Significant Accounting Policies and Recent Developments (Narrative) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Organization, Summary Of Significant Accounting Policies And Recent Developments [Line Items]
Percent voting interest	50.00%
Percent of operating revenues	88.00%
Percent of total assets	99.00%
Allowance for doubtful accounts	$ 900	$ 900
Bad debt expense	500	700	$ 800
Write-offs	500	$ 600	$ 600
Investment	200
Loan to RGRME	1,700
Uncollectible notes receivable	1,700
Noncash impairment charge	$ 200
Minimum [Member]
Organization, Summary Of Significant Accounting Policies And Recent Developments [Line Items]
Estimated useful lives of non-regulated fixed assets	3 years
Maximum [Member]
Organization, Summary Of Significant Accounting Policies And Recent Developments [Line Items]
Estimated useful lives of non-regulated fixed assets	40 years