Income Taxes Income Taxes (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Income Tax Disclosure [Abstract]
Federal income taxes at statutory rates	$ 2,452	$ 3,364	$ 22,721	$ 48,953
Federal income taxes at statutory rates	21.00%	35.00%	21.00%	35.00%
Tax effect of regulatory treatment of utility plant differences	$ (1,521)	$ 742	$ (4,519)	$ 2,244
Tax effect of regulatory treatment of utility plant differences	(13.00%)	7.70%	(4.20%)	1.60%
State income tax expense	$ (319)	$ (301)	$ 694	$ 1,136
State income tax expense	(2.70%)	(3.10%)	0.60%	0.80%
Acquisition costs	$ 122	$ 1,997	$ 241	$ 2,317
Acquisition costs	1.00%	20.80%	0.20%	1.70%
Settlement of equity awards	$ 0	$ 0	$ (990)	$ (1,439)
Settlement of equity awards	(0.00%)	(0.00%)	(0.90%)	(1.00%)
Other	$ 814	$ (649)	$ (680)	$ (1,663)
Other	7.00%	(6.80%)	(0.60%)	(1.20%)
Income Tax Expense (Benefit)	$ 1,548	$ 5,153	$ 17,467	$ 51,548
Effective Income Tax Rate	13.30%	53.60%	16.10%	36.90%