Income Taxes (Narrative) (Details) - USD ($)	1 Months Ended	3 Months Ended	12 Months Ended
	May 31, 2019	Dec. 31, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Taxes [Line Items]
Statutory federal tax rate			21.00%	35.00%	35.00%
Net income tax benefits			$ 66,816,000	$ 64,183,000	$ 84,766,000
Additional net income tax benefits		$ 3,141,000
Effective income tax rate			(6.20%)	(7.70%)	6.60%
Expected tax refund			$ 3,907,000
Unrecognized tax benefits		17,583,000	18,671,000	$ 17,792,000	$ 17,583,000
Deferred income tax liabilities			936,158,000	845,403,000
Interest and penalties		0	0	0	0
Federal [Member]
Income Taxes [Line Items]
Operating loss carryforwards			79,039,000
Operating loss carryforwards, valuation allowance			0
Operating loss carryforwards before unrecognized tax position			152,391,000
Unrecognized tax benefits			73,352,000
State [Member]
Income Taxes [Line Items]
Deferred tax assets operating loss carryforward			817,323,000
Operating loss carryforwards before unrecognized tax position			902,968,000
Unrecognized tax benefits			85,645,000
Pennsylvania [Member]
Income Taxes [Line Items]
Net income tax benefits			$ 31,015,000	$ 26,990,000
Decrease in current taxes payable	$ 16,724,000
Reduction in state income tax expense	158,865,000
Target	3,000,000
Tax deduction	380,000,000
Amortization of benefit	$ 38,000,000
Term	10 years
Deferred income tax liabilities		$ 175,108,000			$ 175,108,000
Minimum [Member]
Income Taxes [Line Items]
State corporate net income tax rates			2.50%
Maximum [Member]
Income Taxes [Line Items]
State corporate net income tax rates			9.99%
Scenario, Plan [Member]
Income Taxes [Line Items]
Statutory federal tax rate			21.00%