Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income	$ 38,806	$ 76,025
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	62,626	65,990
Stock-based compensation	3,880	4,052
Deferred income taxes	9,312	(24,148)
Net gain on sale and impairment of assets	(1,490)	(1,036)
Changes in assets and liabilities which provided/(used) cash:
Accounts receivable, net	4,393	(6,299)
Materials and supplies	(1,972)	2,593
Prepaid expenses and other	819	(7,025)
Accounts payable and accrued expenses	(21,062)	(12,381)
Other assets and liabilities, net	8,077	3,588
Net cash provided by operating activities	103,389	101,359
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchases of property and equipment	(67,788)	(58,222)
Grant proceeds from outside parties	6,495	5,934
Insurance proceeds for replacement of assets	0	1,600
Proceeds from disposition of property and equipment	2,594	1,423
Net cash used in investing activities	(58,699)	(49,265)
CASH FLOWS FROM FINANCING ACTIVITIES:
Principal payments on revolving line-of-credit, long-term debt and finance lease obligations	(155,045)	(121,850)
Proceeds from revolving line-of-credit and long-term borrowings	95,951	176,840
Common share repurchases	(4,796)	(57,376)
Installment payments on Freightliner deferred consideration	0	(6,255)
Other financing related activities, net	(1,989)	(1,973)
Net cash used in financing activities	(65,879)	(10,614)
EFFECT OF EXCHANGE RATE CHANGES ON CASH AND CASH EQUIVALENTS	910	(562)
(DECREASE)/INCREASE IN CASH AND CASH EQUIVALENTS	(20,279)	40,918
CASH AND CASH EQUIVALENTS, beginning of period	90,387	80,472
CASH AND CASH EQUIVALENTS, end of period	$ 70,108	$ 121,390