Long-Term Debt (2018 Revolving Credit Agreement) (Details) - USD ($)	Mar. 06, 2020	Sep. 26, 2019	Aug. 17, 2018	Jun. 30, 2020	Dec. 31, 2019
Revolving Credit Facility
Debt Instrument [Line Items]
Maximum borrowing capacity	$ 100,000,000.0		$ 50,000,000.0
Borrowing base			85.00%
Unused capacity, commitment fee rate	0.25%
Debt covenant, total commitments (as a percent)	12.50%
Debt covenant, commitment	$ 10,000,000.0
Fixed charge coverage ratio	1.0
Letters of credit outstanding				$ 66,100,000	$ 2,900,000
Revolving Credit Facility | Minimum
Debt Instrument [Line Items]
Unused capacity, commitment fee rate			0.25%
Revolving Credit Facility | Maximum
Debt Instrument [Line Items]
Unused capacity, commitment fee rate			0.375%
Revolving Credit Facility | London Interbank Offered Rate | Minimum
Debt Instrument [Line Items]
Basis spread on variable rate			1.25%
Revolving Credit Facility | London Interbank Offered Rate | Maximum
Debt Instrument [Line Items]
Basis spread on variable rate			1.75%
Revolving Credit Facility | Alternative Base Rate
Debt Instrument [Line Items]
Basis spread on variable rate	1.00%
Revolving Credit Facility | Alternative Base Rate | Minimum
Debt Instrument [Line Items]
Basis spread on variable rate			0.25%
Revolving Credit Facility | Alternative Base Rate | Maximum
Debt Instrument [Line Items]
Basis spread on variable rate			0.75%
Revolving Credit Facility | Federal Funds Rate
Debt Instrument [Line Items]
Basis spread on variable rate		0.50%	0.50%
Revolving Credit Facility | Prime Rate
Debt Instrument [Line Items]
Basis spread on variable rate			1.00%
Letter of Credit
Debt Instrument [Line Items]
Maximum borrowing capacity	$ 10,000,000.0		$ 10,000,000.0