Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income	$ 132,203	$ 140,103
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	151,095	138,568
Stock-based compensation	13,835	10,341
Excess tax benefit from share-based compensation	(25)	(1,393)
Deferred income taxes	25,088	46,795
Net loss/(gain) on sale and impairment of assets	11,993	(1,981)
Insurance proceeds received	0	103
Loss on settlement of foreign currency forward purchase contracts	0	18,686
Changes in assets and liabilities which provided/(used) cash, net of effect of acquisitions:
Accounts receivable, net	(10,731)	52,847
Materials and supplies	(2,642)	(2,325)
Prepaid expenses and other	(1,930)	14,929
Accounts payable and accrued expenses	(29,484)	(71,446)
Other assets and liabilities, net	14,156	(970)
Net cash provided by operating activities	303,558	344,257
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchase of property and equipment	(159,523)	(276,150)
Grant proceeds from outside parties	29,952	31,456
Cash paid for acquisitions, net of cash acquired	0	(735,556)
Net payment from settlement of foreign currency forward purchase contracts related to an acquisition	0	(18,686)
Insurance proceeds for the replacement of assets	10,319	9,658
Proceeds from disposition of property and equipment	2,003	3,223
Net cash used in investing activities	(117,249)	(986,055)
CASH FLOWS FROM FINANCING ACTIVITIES:
Principal payments on revolving line-of-credit, long-term debt and capital lease obligations	(501,087)	(502,839)
Proceeds from revolving line-of-credit and long-term borrowings	300,495	1,139,511
Debt amendment/issuance costs	0	(9,622)
Proceeds from employee stock purchases	5,969	5,478
Treasury stock purchases	(3,065)	(3,245)
Excess tax benefit from share-based compensation	25	1,393
Net cash (used in)/provided by financing activities	(197,663)	630,676
EFFECT OF EXCHANGE RATE CHANGES ON CASH AND CASH EQUIVALENTS	1,779	(9,632)
DECREASE IN CASH AND CASH EQUIVALENTS	(9,575)	(20,754)
CASH AND CASH EQUIVALENTS, beginning of period	35,941	59,727
CASH AND CASH EQUIVALENTS, end of period	$ 26,366	$ 38,973