Segment Information (Revenue By Geographic Area) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues	$ 535,548	$ 470,068	$ 1,017,866	$ 871,004
Long-lived assets	1,240,703		1,240,703		$ 1,316,944
United States [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues	447,666	402,065	855,213	735,674
Long-lived assets	1,001,738		1,001,738		1,064,823
International [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues	87,882	$ 68,003	162,653	$ 135,330
Long-lived assets	$ 238,965		$ 238,965		$ 252,121