Segment Information (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Segment Reporting Information [Line Items]
Operating revenues	$ 124,567	$ 134,476	$ 388,202	$ 430,200
Depreciation and amortization	21,147	20,224	42,022	40,177
Income (loss) from operations	8,269	16,435	76,020	95,516
Net income (loss) from continuing operations	(339)	4,075	41,672	45,472
Capital expenditures			102,370	94,333
Total Assets	2,986,760	3,065,154	2,986,760	3,065,154	$ 3,039,746
Utility
Segment Reporting Information [Line Items]
Operating revenues	118,515		376,448
Other
Segment Reporting Information [Line Items]
Operating revenues	6,052		11,754
Operating Segments | Utility
Segment Reporting Information [Line Items]
Operating revenues	118,515	130,095	376,448	422,821
Depreciation and amortization	20,766	19,894	41,309	39,518
Income (loss) from operations	4,545	13,158	69,301	90,285
Net income (loss) from continuing operations	(2,970)	2,137	36,913	42,329
Capital expenditures	43,801	54,265	100,695	93,119
Total Assets	2,907,724	2,792,011	2,907,724	2,792,011	2,961,326
Operating Segments | Other
Segment Reporting Information [Line Items]
Operating revenues	6,052	4,381	11,754	7,379
Depreciation and amortization	381	330	713	659
Income (loss) from operations	3,724	3,277	6,719	5,231
Net income (loss) from continuing operations	2,631	1,938	4,759	3,143
Capital expenditures	1,239	1,142	1,675	1,214
Total Assets	66,293	66,139	66,293	66,139	64,546
Operating Segments | Total Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues	124,567	134,476	388,202	430,200
Depreciation and amortization	21,147	20,224	42,022	40,177
Income (loss) from operations	8,269	16,435	76,020	95,516
Net income (loss) from continuing operations	(339)	4,075	41,672	45,472
Capital expenditures	45,040	55,407	102,370	94,333
Total Assets	$ 2,974,017	$ 2,858,150	$ 2,974,017	$ 2,858,150	$ 3,025,872