Property and Equipment, Net (Narrative) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Property and Equipment [Line Items]
Capitalized internal-use software, gross	$ 122,000	$ 109,900
Capitalized internal-use software, net	26,500	23,500
Depreciation and amortization	212,930	188,049	$ 164,915
Property and Equipment [Member]
Property and Equipment [Line Items]
Depreciation and amortization	$ 192,300	$ 167,200	$ 143,600