Basis of Presentation and Significant Accounting Policies - Self-Generation Incentive Program (SGIP) (Additional Information) (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Accounting Policies [Abstract]
Self-Generation Incentive Program, percentage of incentive issued in the first year			50.00%
Self-Generation Incentive Program, subsequent payment period			5 years
Self-Generation Incentive Program, operational criteria period			5 years
SGIP funds received	$ 200,000	$ 300,000	$ 1,000,000	$ 2,000,000
Reductions or refunds of SGIP funds	0	0	0	0
Accrual for refund of incentives	$ 0	$ 0	$ 0	$ 0