Lease Obligations (Schedule of Future Minimum Lease Commitments) (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Finance Leases
2020	$ 122,400
2021	107,900
2022	67,400
2023	21,400
2024	1,100
Thereafter	0
Total minimum lease payments	320,200
Less amounts representing interest	(18,900)
Total lease obligations, net of interest	301,300
Less current portion	(111,600)
Long-term portion of lease obligations, net of interest	189,700
Operating Leases
2020	88,800
2021	65,900
2022	41,600
2023	20,200
2024	12,800
Thereafter	28,700
Total minimum lease payments	258,000
Less amounts representing interest	(21,800)
Total lease obligations, net of interest	236,200
Less current portion	81,561	$ 0
Long-term operating lease liabilities	$ 154,553	$ 0