Basis of Presentation and Significant Accounting Policies - Self-Generation Incentive Program (SGIP) (Additional Information) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
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	$ 1,900,000	$ 2,700,000	$ 3,300,000
Reductions or refunds of SGIP funds	0	$ 0	$ 0
Accrual for refund of incentives	$ 0