Acquisitions (Pro- Forma) (Details) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended	9 Months Ended
Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Business Acquisition, Pro Forma Information [Abstract]
Revenues	$ 713,082	$ 644,121	$ 2,116,998	$ 1,851,618
Income from operations	87,173	69,483	218,735	208,150
Net income	$ 76,364	$ 70,039	$ 199,350	$ 214,784
Per share - basic (in dollars per share)	$ 0.41	$ 0.37	$ 1.07	$ 1.15
Per share - diluted (in dollars per share)	$ 0.40	$ 0.37	$ 1.06	$ 1.13

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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