Lease Obligations (Schedule of Future Minimum Lease Commitments) (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Finance Leases
2020, remaining three months	$ 41,600
2021	131,700
2022	91,500
2023	38,900
2024	6,400
Thereafter	200
Total minimum lease payments	310,300
Less amounts representing interest	(15,200)
Total lease obligations, net of interest	295,100
Less current portion	128,900
Long-term portion of lease obligations, net of interest	166,200
Operating Leases
2020, remaining three months	29,400
2021	72,600
2022	46,500
2023	23,800
2024	15,600
Thereafter	30,000
Total minimum lease payments	217,900
Less amounts representing interest	(17,900)
Total lease obligations, net of interest	200,000
Less current portion	74,439	$ 81,561
Long-term portion of lease obligations, net of interest	$ 125,639	$ 154,553