Consolidated Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income	$ 22,241	$ 22,122
Adjustments to reconcile net income to net cash provided by operating activities:
Loss from discontinued operations	3	0
Depreciation and amortization	17,633	15,861
Compensation cost related to equity awards	2,290	2,148
Excess tax benefit from share-based compensation	(1,746)	(900)
Deferred income taxes	9,977	3,311
Net gain on sale of assets	(1,230)	(1,010)
Insurance proceeds received	12,521	0
Changes in assets and liabilities which provided (used) cash, net of effect of acquisitions:
Accounts receivable, net	(2,526)	(13,837)
Materials and supplies	(1,418)	(656)
Prepaid expenses and other	(2,496)	(1,535)
Accounts payable and accrued expenses	(27,491)	(20,039)
Other assets and liabilities, net	(9)	1,819
Net cash provided by operating activities from continuing operations	27,749	7,284
Net cash used in operating activities from discontinued operations	(3)	(4)
Net cash provided by operating activities	27,746	7,280
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchase of property and equipment	(50,318)	(15,725)
Grant proceeds from outside parties	8,437	7,514
Cash paid for acquisitions, net of cash acquired	(837)	(440)
Proceeds from disposition of property and equipment	1,626	1,031
Net cash used in investing activities from continuing operations	(41,092)	(7,620)
CASH FLOWS FROM FINANCING ACTIVITIES:
Principal payments on long-term borrowings, including capital leases	(56,461)	(55,981)
Proceeds from issuance of long-term debt	64,716	52,967
Proceeds from employee stock purchases	6,210	4,006
Treasury stock purchases	(1,757)	(1,029)
Excess tax benefit from share-based compensation	1,746	900
Net cash provided by financing activities from continuing operations	14,454	863
EFFECT OF EXCHANGE RATE CHANGES ON CASH AND CASH EQUIVALENTS	361	(897)
CHANGE IN CASH BALANCES INCLUDED IN CURRENT ASSETS OF DISCONTINUED OPERATIONS	0	1
INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	1,469	(373)
CASH AND CASH EQUIVALENTS, beginning of period	27,269	27,417
CASH AND CASH EQUIVALENTS, end of period	$ 28,738	$ 27,044