Segment Information (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Debt Instrument [Line Items]
Cash	$ 15,200		$ 15,200		$ 1,700
Long-term nonutility investments	5,100		$ 5,100		$ 5,200
Nonutility assets representation rate (percentage, less than)			1.00%		1.00%
Net income	30,072	$ (5,265)	$ 57,477	$ 16,944
Utility Segment [Member]
Debt Instrument [Line Items]
Net income	$ 36,400	$ 15,300	$ 70,100	$ 45,000