Consolidated Statements of Cash Flows (USD $)	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income	$ 39,634,000	$ 82,728,000
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	37,641,000	34,223,000
Compensation cost related to equity awards	3,314,000	7,525,000
Excess tax benefit from share-based compensation	(3,580,000)	(4,314,000)
Deferred income taxes	16,118,000	(33,866,000)
Net gain on sale of assets	(838,000)	(1,707,000)
Insurance proceeds received	0	9,315,000
Changes in assets and liabilities which provided/(used) cash, net of effect of acquisitions:
Accounts receivable, net	(8,559,000)	(8,766,000)
Materials and supplies	131,000	(3,404,000)
Prepaid expenses and other	2,181,000	(2,215,000)
Accounts payable and accrued expenses	(15,582,000)	(15,328,000)
Other assets and liabilities, net	1,200,000	628,000
Net cash provided by operating activities	71,660,000	64,819,000
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchase of property and equipment	(71,618,000)	(37,908,000)
Grant proceeds from outside parties	12,800,000	2,848,000
Insurance proceeds for the replacement of assets	300,000	0
Proceeds from disposition of property and equipment	1,555,000	2,011,000
Net cash used in investing activities	(56,963,000)	(33,049,000)
CASH FLOWS FROM FINANCING ACTIVITIES:
Principal payments on long-term borrowings, including capital leases	(96,287,000)	(139,475,000)
Proceeds from issuance of long-term debt	46,546,000	73,362,000
Debt amendment costs	0	(1,543,000)
Proceeds from employee stock purchases	4,647,000	5,903,000
Treasury stock purchases	(3,374,000)	(7,237,000)
Dividends paid on Series A-1 Preferred Stock	0	(2,139,000)
Excess tax benefit from share-based compensation	3,580,000	4,314,000
Net cash used in financing activities	(44,888,000)	(66,815,000)
EFFECT OF EXCHANGE RATE CHANGES ON CASH AND CASH EQUIVALENTS	(498,000)	(391,000)
DECREASE IN CASH AND CASH EQUIVALENTS	(30,689,000)	(35,436,000)
CASH AND CASH EQUIVALENTS, beginning of period	62,876,000	64,772,000
CASH AND CASH EQUIVALENTS, end of period	$ 32,187,000	$ 29,336,000