Segment Reporting (Revenue by Geographical Areas) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Revenues from External Customers [Line Items]
Revenues	$ 653,313	$ 608,088	$ 1,279,841	$ 1,190,128
Revenue as Percentage of Consolidated Revenue	100.00%	100.00%	100.00%	100.00%
Domestic [Member]
Revenues from External Customers [Line Items]
Revenues	$ 620,682	$ 578,165	$ 1,216,983	$ 1,132,603
Revenue as Percentage of Consolidated Revenue	95.00%	95.10%	95.10%	95.20%
Foreign [Member]
Revenues from External Customers [Line Items]
Revenues	$ 32,631	$ 29,923	$ 62,858	$ 57,525
Revenue as Percentage of Consolidated Revenue	5.00%	4.90%	4.90%	4.80%