Business Combinations (Details 3) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended	6 Months Ended
Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Summary of unaudited consolidated pro forma results of operations
Revenues	$ 3,704,215	$ 3,408,230	$ 7,121,402	$ 6,661,073
Income from continuing operations	64,528	52,803	121,614	103,517
Net income	$ 62,092	$ 51,128	$ 119,659	$ 98,709
Income from continuing operations per diluted common share (in dollars per share)	$ 0.71	$ 0.58	$ 1.34	$ 1.14
Net income per diluted common share (in dollars per share)	$ 0.69	$ 0.57	$ 1.32	$ 1.09

The pro forma diluted net income per share for a period as if the business combination or combinations had been completed at the beginning of a period.

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-Name Statement of Financial Accounting Standard (FAS)

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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