Income Taxes (Details) - USD ($) $ in Thousands		12 Months Ended
	May 01, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Operating Loss Carryforwards [Line Items]
Effective Income Tax Rate Reconciliation at Federal Statutory Income Tax Rate, Amount		$ 47,834	$ 55,800	$ 148,847
Effective Income Tax Rate Reconciliation, Nondeductible Expense, Depreciation and Amortization, Amount		(23,025)	(25,871)	0
Income Tax Reconciliation, AFUDC (net)		(4,462)	(4,173)	(4,506)
Income Tax Reconciliation, Executive Compensation		2,596	4,439	0
Income Tax Reconciliation, Treasury Grant		(7,870)	(4,861)	(9,537)
Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Amount		0	0	117,185
Effective Income Tax Rate Reconciliation, Other Adjustments, Amount		2,000	4,758	3,154
Income tax (benefit) expense		$ 17,073	$ 30,092	$ 255,143
Effective Income Tax Rate Reconciliation, Percent		7.50%	11300.00%	60000.00%
Subsidiaries [Member]
Operating Loss Carryforwards [Line Items]
Effective Income Tax Rate Reconciliation at Federal Statutory Income Tax Rate, Amount		$ 69,735	$ 77,251	$ 185,430
Effective Income Tax Rate Reconciliation, Nondeductible Expense, Depreciation and Amortization, Amount		(23,025)	(25,871)	0
Income Tax Reconciliation, AFUDC (net)		(4,462)	(4,173)	(4,506)
Income Tax Reconciliation, Executive Compensation		2,596	4,439	0
Income Tax Reconciliation, Treasury Grant		(7,870)	(4,861)	(9,537)
Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Amount		0	0	36,328
Effective Income Tax Rate Reconciliation, Other Adjustments, Amount		2,174	3,915	4,271
Income tax (benefit) expense	$ 34,600	$ 39,148	$ 50,700	$ 211,986
Effective Income Tax Rate Reconciliation, Percent		11.80%	13.80%	40.00%