Lease Accounting (Maturity of Lease Liabilities) (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Jan. 01, 2019
Operating Leased Assets [Line Items]
2019	$ 32,394
2020	38,053
2022	29,270
Lessee, Operating Lease, Liability, Payments, Due Year Four	25,652
2023	23,024
Thereafter	175,011
Total Lease Payments	323,404
Less: Interest	(128,195)
Total Lease Liability	195,209	$ 204,364
Transportation Equipment
Operating Leased Assets [Line Items]
2019	20,898
2020	24,621
2022	19,483
Lessee, Operating Lease, Liability, Payments, Due Year Four	17,880
2023	17,077
Thereafter	43,619
Total Lease Payments	143,578
Less: Interest	(26,689)
Total Lease Liability	116,889
Office Space & Equipment
Operating Leased Assets [Line Items]
2019	3,088
2020	4,049
2022	3,067
Lessee, Operating Lease, Liability, Payments, Due Year Four	2,362
2023	598
Thereafter	2,307
Total Lease Payments	15,471
Less: Interest	(2,117)
Total Lease Liability	13,354
Facilities and Equipment
Operating Leased Assets [Line Items]
2019	8,408
2020	9,383
2022	6,720
Lessee, Operating Lease, Liability, Payments, Due Year Four	5,410
2023	5,349
Thereafter	129,085
Total Lease Payments	164,355
Less: Interest	(99,389)
Total Lease Liability	$ 64,966