Lease Obligations (Schedule of Future Minimum Lease Commitments) (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Finance Leases
2020, remaining nine months	$ 96,600
2021	115,000
2022	74,600
2023	26,900
2024	3,000
Thereafter	0
Total minimum lease payments	316,100
Less amounts representing interest	(17,900)
Total lease obligations, net of interest	298,200
Less current portion	116,900
Long-term portion of lease obligations, net of interest	181,300
Operating Leases
2020, remaining nine months	66,800
2021	68,200
2022	43,300
2023	21,200
2024	13,800
Thereafter	30,600
Total minimum lease payments	243,900
Less amounts representing interest	(20,400)
Total lease obligations, net of interest	223,500
Less current portion	80,076	$ 81,561
Long-term portion of lease obligations, net of interest	$ 143,441	$ 154,553