Acquisitions (Pro- Forma) (Details) (Details) (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
Business Acquisition, Pro Forma Information [Abstract]
Revenues	$ 730,384	$ 616,854	$ 1,403,344	$ 1,207,346
Income from operations	75,888	70,176	132,230	139,293
Net income	$ 64,461	$ 84,314	$ 123,980	$ 145,114
Per share - basic (in dollars per share)	$ 0.34	$ 0.45	$ 0.66	$ 0.78
Per share - diluted (in dollars per share)	$ 0.34	$ 0.45	$ 0.66	$ 0.77

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

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 805

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (h)(2)-(3)

-URI http://asc.fasb.org/extlink&oid=25497992&loc=d3e1392-128463

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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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- Definition

The pro forma income from continuing operations before changes in accounting and extraordinary items, net of tax effect, for the period as if the business combination or combinations had been completed at the beginning of a period.

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The pro forma net Income or Loss for the period as if the business combination or combinations had been completed at the beginning of a period.

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The pro forma revenue for a period as if the business combination or combinations had been completed at the beginning of the period.

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