Revenue (Details) - USD ($) $ in Thousands	3 Months Ended			6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Disaggregation of Revenue [Line Items]
Contract with Customer, Asset, Gross	$ 150,700			$ 150,700		$ 160,800
Revenue from Contract with Customer, Excluding Assessed Tax	332,900	$ 354,400		709,000	$ 703,700
REVENUES	340,869	359,678		723,178	714,182
Retail Revenue [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	319,991	333,695		686,494	679,256
Other non-606 revenue	7,697	4,006		12,590	7,864
Wholesale Revenue [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	10,006	17,652		17,107	19,163
Miscellaneous revenue [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	2,898	3,033		5,383	5,275
Other non-606 revenue	277	1,292		1,604	2,624
Electricity [Member]
Disaggregation of Revenue [Line Items]
REVENUES	$ 340,869	$ 359,678	$ 714,182	$ 723,178	$ 714,182