Segments and Related Information (Foreign Operations) (Narrative) (Details) - USD ($) $ in Thousands				3 Months Ended								12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Segment and Related Information [Line Items]
Revenue				$ 1,709,300	$ 2,016,600	$ 1,939,000	$ 1,518,300	$ 1,917,600	$ 1,977,200	$ 1,617,800	$ 1,396,800	$ 7,183,188	$ 6,909,417	$ 6,606,978
Property and equipment, net	$ 905,835	$ 747,808		905,835				747,808				905,835	747,808
Intangible assets and goodwill, net	1,433,000	1,269,700		1,433,000				1,269,700				1,433,000	1,269,700
United States [Member]
Segment and Related Information [Line Items]
Revenue												6,900,000	6,700,000	6,400,000
Property and equipment, net	874,700	707,400	$ 649,500	874,700				707,400				874,700	707,400	649,500
Intangible assets and goodwill, net	1,400,000	1,200,000	1,200,000	1,400,000				1,200,000				1,400,000	1,200,000	1,200,000
Foreign Operations [Member]
Segment and Related Information [Line Items]
Revenue												233,500	164,300	211,500
Property and equipment, net	31,100	40,400	57,000	31,100				40,400				31,100	40,400	57,000
Intangible assets and goodwill, net	$ 56,400	$ 61,500	$ 112,800	$ 56,400				$ 61,500				$ 56,400	$ 61,500	$ 112,800
Foreign Operations [Member] | Accounts Receivable, Net, Less Deferred Revenue [Member] | Geographic Concentration Risk [Member]
Segment and Related Information [Line Items]
Concentration risk, percentage of total	5.00%	5.00%	5.00%
Government [Member] | Revenue Benchmark [Member] | Customer Concentration Risk [Member]
Segment and Related Information [Line Items]
Concentration risk, percentage of total												1.00%	1.00%	1.00%