Statements of Cash Flows (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
CASH FLOWS FROM INVESTING ACTIVITIES:
Utility plant additions, debt portion of allowance for funds used during construction	$ 483	$ 127	$ 115
Supplemental disclosure of non-cash investing and financing activities:
Accounts payable, construction of utility plant	$ 1,498	$ 2,766	$ 720