Acquisitions and Other Investments (Schedule of Business Acquisitions, Consideration Paid and Purchase Price Allocation) (Details) (USD $)	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2012	Dec. 31, 2011	May 02, 2013 Big Country [Member]	May 02, 2013 Big Country [Member] Backlog [Member]	May 02, 2013 Big Country [Member] Noncompete Agreements [Member]	May 02, 2013 Big Country [Member] Customer Relationships [Member]	May 02, 2013 Big Country [Member] Pre-Qualifications [Member]	May 02, 2013 Big Country [Member] Other Current Assets [Member]	May 02, 2013 Big Country [Member] Accrued Liabilities [Member]	May 02, 2013 Big Country [Member] Long-term Debt [Member]	May 02, 2013 Big Country [Member] Deferred Income Tax Charges [Member]	May 02, 2013 Big Country [Member] Earn-out Arrangements [Member]	Dec. 02, 2012 Bottom Line Services [Member]	Dec. 02, 2012 Bottom Line Services [Member] Trade Names [Member]	Dec. 02, 2012 Bottom Line Services [Member] Noncompete Agreements [Member]	Dec. 02, 2012 Bottom Line Services [Member] Customer Relationships [Member]	Dec. 02, 2012 Bottom Line Services [Member] Other Current Assets [Member]	Dec. 02, 2012 Bottom Line Services [Member] Accrued Liabilities [Member]	Dec. 02, 2012 Bottom Line Services [Member] Earn-out Arrangements [Member]
Purchase price consideration:
Acquisition payments in cash					$ 103,500,000										$ 67,600,000
Estimated fair value of contingent consideration														22,800,000							11,100,000
Total consideration transferred					126,300,000										78,700,000
Purchase price allocation to identifiable assets acquired and liabilities assumed:
Assets										69,000,000									36,300,000
Property and equipment					42,600,000										12,600,000
Intangible assets						10,100,000	1,800,000	6,500,000	29,600,000							2,600,000	500,000	24,400,000
Liabilities											(21,900,000)	(24,400,000)	(10,100,000)							(12,800,000)
Total identifiable net assets					94,900,000										63,600,000
Goodwill	860,207,000	826,110,000	718,300,000	714,800,000	31,400,000										15,100,000
Total consideration allocated					$ 126,300,000										$ 78,700,000