Lease Accounting (Major Categories of Operating Lease Portfolio) (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Jan. 01, 2019	Dec. 31, 2018
Operating Leased Assets [Line Items]
Total Right of Use Assets, net	$ 191,497	$ 208,929	$ 0
Accrued liabilities, current	30,501	33,016
Other long-term liabilities, non-current	157,228	171,348
Total Lease Liability	187,729	204,364
Transportation Equipment
Operating Leased Assets [Line Items]
Total Right of Use Assets, net	107,383	117,727
Total Lease Liability	111,827
Office Space & Equipment
Operating Leased Assets [Line Items]
Total Right of Use Assets, net	12,517	14,194
Total Lease Liability	12,587
Facilities and Equipment
Operating Leased Assets [Line Items]
Total Right of Use Assets, net	71,597	$ 77,008
Total Lease Liability	$ 63,315