Consolidated Statements of Cash Flows - USD ($)	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income	$ 140,103,000	$ 173,382,000
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	138,568,000	116,130,000
Stock-based compensation	10,341,000	9,063,000
Excess tax benefit from share-based compensation	(1,393,000)	(5,483,000)
Deferred income taxes	46,795,000	62,612,000
Net gain on sale of assets	(1,981,000)	(3,444,000)
Loss on settlement of foreign currency forward purchase contracts	18,686,000	0
Insurance proceeds received	103,000	5,527,000
Changes in assets and liabilities which provided/(used) cash, net of effect of acquisitions:
Accounts receivable, net	52,847,000	(32,222,000)
Materials and supplies	(2,325,000)	(1,070,000)
Prepaid expenses and other	14,929,000	5,568,000
Accounts payable and accrued expenses	(71,446,000)	34,990,000
Other assets and liabilities, net	(970,000)	3,950,000
Net cash provided by operating activities	344,257,000	369,003,000
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchase of property and equipment	(276,150,000)	(271,696,000)
Grant proceeds from outside parties	31,456,000	43,518,000
Cash paid for acquisitions, net of cash acquired	(735,556,000)	(220,542,000)
Net payment from settlement of foreign currency forward purchase contracts related to an acquisition	(18,686,000)	0
Insurance proceeds for the replacement of assets	9,658,000	4,112,000
Proceeds from disposition of property and equipment	3,223,000	4,562,000
Net cash used in investing activities	(986,055,000)	(440,046,000)
CASH FLOWS FROM FINANCING ACTIVITIES:
Principal payments on long-term borrowings, including capital leases	(502,839,000)	(378,763,000)
Proceeds from issuance of long-term debt	1,139,511,000	398,761,000
Debt amendment/issuance costs	(9,622,000)	(3,880,000)
Proceeds from employee stock purchases	5,478,000	9,574,000
Treasury stock purchases	(3,245,000)	(4,062,000)
Excess tax benefit from share-based compensation	1,393,000	5,483,000
Net cash provided by financing activities	630,676,000	27,113,000
EFFECT OF EXCHANGE RATE CHANGES ON CASH AND CASH EQUIVALENTS	(9,632,000)	(154,000)
DECREASE IN CASH AND CASH EQUIVALENTS	(20,754,000)	(44,084,000)
CASH AND CASH EQUIVALENTS, beginning of period	59,727,000	62,876,000
CASH AND CASH EQUIVALENTS, end of period	$ 38,973,000	$ 18,792,000