Supplemental Cash Flow Information - Supplemental Cash Flow Information and Non-cash Investing and Financing Activities (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Supplemental cash flow information
Cash paid during the period for interest	$ 33,972	$ 25,850	$ 29,981
Cash (received) paid during the period for taxes		(31)	75
Non-cash investing and financing activities
Non-cash right of way additions to electric plant			337
Change in accrued additions to electric plant	4,113	6,942	20,633
Allowance for funds used during construction - debt	3,142	1,767	1,635
Net non-cash equity issuances related to the Merger and Reorganization		97,193
Net non-cash noncontrolling equity issuances related to the Merger and Reorganization		119,607
Redemption of operating partnership units for common stock	3,277
Non-cash noncontrolling interest equity issuances		755	4,648
Dividends and distributions payable	$ 15,161	$ 13,634	$ 14,130