Consolidated Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
CASH FLOWS FROM OPERATING ACTIVITIES:[Abstract]
Net income	$ 119,484	$ 81,260	$ 61,473
Adjustments to reconcile net income to net cash provided by operating activities: [Abstract]
Loss/(income) from discontinued operations	9	(2,591)	(1,398)
Depreciation and amortization	66,481	51,166	48,110
Compensation cost related to equity awards	7,776	7,174	6,031
Excess tax benefit from share-based compensation	(2,820)	(1,975)	(1,234)
Deferred income taxes	26,291	12,009	7,558
Stamp duty	0	12,625	0
Net (gain)/loss on sale and impairment of assets	(5,660)	(6,441)	3,953
Gain on sale of investments	907	0	391
Gain on insurance recoveries	(1,061)	0	(3,143)
Insurance proceeds received	646	0	2,175
Changes in assets and liabilities which provided (used) cash, net of effect of acquisitions:
Accounts receivable, net	(12,307)	(18,402)	16,082
Materials and supplies	(1,206)	(205)	(170)
Prepaid expenses and other	3,543	(762)	(622)
Accounts payable and accrued expenses	(25,556)	36,243	(10,940)
Other assets and liabilities, net	(1,235)	1,651	(550)
Net cash provided by operating activities from continuing operations	173,478	171,752	126,934
Net cash (used in)/provided by operating activities from discontinued operations	(13)	933	(746)
Net cash provided by operating activities	173,465	172,685	126,188
CASH FLOWS FROM INVESTING ACTIVITIES: [Abstract]
Purchase of property and equipment	(178,668)	(119,840)	(88,865)
Grant proceeds from outside parties	(22,642)	(40,802)	(24,575)
Cash paid for acquisition, net of cash acquired	(89,935)	(320,023)	(5,780)
Insurance proceeds for the replacement of assets	0	0	3,996
Proceeds from sale of investments	1,369	208	3,778
Proceeds from disposition of property and equipment	9,464	9,991	8,313
Net cash used in investing activities from continuing operations	(235,128)	(388,862)	(53,983)
Net cash provided by investing activities from discontinued operations	0	1,831	1,774
Net cash used in investing activities	(235,128)	(387,031)	(52,209)
CASH FLOWS FROM FINANCING ACTIVITIES: [Abstract]
Principal payments on long-term borrowings, including capital leases	(533,544)	(82,296)	(214,153)
Proceeds from issuance of long-term debt	581,394	205,446	98,000
Debt amendment/issuance costs	(4,742)	(2,514)	0
Proceeds from employee stock purchases	17,433	18,205	5,765
Treasury stock acquisitions	(1,326)	(850)	(434)
Stock issuance proceeds, net of stock issuance costs	0	0	106,614
Cash paid for change in ownership of noncontrolling interest	0	0	(4,360)
Excess tax benefit from share-based compensation	2,820	1,975	1,234
Net cash provided by/(used in) financing activities from continuing operations	62,035	139,966	(7,334)
EFFECT OF EXCHANGE RATE CHANGES ON CASH AND CASH EQUIVALENTS	(521)	(4,009)	6,831
CHANGE IN CASH BALANCES INCLUDED IN CURRENT ASSETS OF DISCONTINUED OPERATIONS	1	99	538
(DECREASE) INCREASE IN CASH AND CASH EQUIVALENTS	(148)	(78,290)	74,014
CASH AND CASH EQUIVALENTS, beginning of year	27,417	105,707	31,693
CASH AND CASH EQUIVALENTS, end of year	$ 27,269	$ 27,417	$ 105,707