Lease Obligations (Schedule of Future Minimum Lease Commitments) (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Finance Leases
2020, remaining six months	$ 66,800
2021	120,000
2022	79,600
2023	31,200
2024	4,800
Thereafter	300
Total minimum lease payments	302,700
Less amounts representing interest	(16,200)
Total lease obligations, net of interest	286,500
Less current portion	119,100
Long-term portion of lease obligations, net of interest	167,400
Operating Leases
2020, remaining six months	50,400
2021	69,800
2022	44,500
2023	21,700
2024	13,900
Thereafter	29,100
Total minimum lease payments	229,400
Less amounts representing interest	(17,900)
Total lease obligations, net of interest	211,500
Less current portion	78,044	$ 81,561
Long-term portion of lease obligations, net of interest	$ 133,535	$ 154,553