Income Taxes (Details) - USD ($)	6 Months Ended		12 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Income Tax Disclosure [Abstract]
Unrecognized Tax Benefits	$ 12,500,000		$ 12,000,000.0
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent	21.00%	21.00%
Effective Income Tax Rate Reconciliation, State and Local Income Taxes, Percent	3.70%	3.70%
Effective Income Tax Rate Reconciliation, Tax Credit, Percent	(9.80%)	(9.40%)
Effective Income Tax Rate Reconciliation, Other Regulatory Items, Percent	(4.70%)	(3.40%)
Regulatory differences - reversal of prior quarters' ARAM deferral (b)	(1.10%)	(1.00%)
Effective Income Tax Rate Reconciliation, Other Adjustments, Percent	0.50%	0.10%
Effective Income Tax Rate Reconciliation, Percent	9.60%	11.00%
Unrecognized Tax Benefits [Abstract]
Unrecognized tax benefit — Permanent tax positions	$ 8,000,000.0		7,400,000
Unrecognized tax benefit — Temporary tax positions	4,500,000		4,600,000
Total unrecognized tax benefit	12,500,000		12,000,000.0
NOL and tax credit carryforwards	(8,100,000)		(8,300,000)
Net Deferred Tax Liability associated with the Unrecognized Tax Benefit Amounts and Related NOLs and Tax Credit Carryforwards	(5,700,000)		(5,000,000.0)
Upper bound of decrease in unrecognized tax benefit that is reasonably possible	7,600,000
Amounts accrued for penalties related to unrecognized tax benefits	0		0
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Payable for interest related to unrecognized tax benefits at beginning of period	(1,100,000)	$ (700,000)	(700,000)
Interest expense related to unrecognized tax benefits	(900,000)		(400,000)
Payable for interest related to unrecognized tax benefits at end of period	(2,000,000.0)		$ (1,100,000)
Income Tax Examination [Line Items]
Income Tax Credits and Adjustments	$ 0