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Segment Reporting (Revenue by Geographical Areas) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Revenues from External Customers [Line Items]
Revenues	$ 878,509	$ 653,313	$ 1,563,682	$ 1,279,841
Revenue as Percentage of Consolidated Revenue	100.00%	100.00%	100.00%	100.00%
Domestic [Member]
Revenues from External Customers [Line Items]
Revenues	$ 837,972	$ 620,682	$ 1,485,239	$ 1,216,983
Revenue as Percentage of Consolidated Revenue	95.40%	95.00%	95.00%	95.10%
Foreign [Member]
Revenues from External Customers [Line Items]
Revenues	$ 40,537	$ 32,631	$ 78,443	$ 62,858
Revenue as Percentage of Consolidated Revenue	4.60%	5.00%	5.00%	4.90%

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- Definition

Revenue as percentage of consolidated revenue

+ References

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Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 22
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=115929826&loc=d3e8736-108599

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
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-URI http://asc.fasb.org/extlink&oid=115205541&loc=SL114868664-224227

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
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-Section 50
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Reference 4: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
-Topic 280
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