Income Taxes (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017
Income Taxes [Line Items]
Income tax (benefit) expense	$ (987)	$ 5
Decrease in operating tax benefit	700	200
Decrease in non-operating income tax expense	1,600	$ 800
Benefit from decrease in corporate federal tax rate	1,500
Ratepayer net refund				$ 108,000
Unrecognized tax benefits	11,300			10,500
Tax benefits that, if recognized, would affect the effective tax rate	$ 2,100			$ 2,300
Scenario, Forecast
Income Taxes [Line Items]
Effective tax rate estimate			(23.00%)