Property and Equipment, Net (Narrative) (Details) - USD ($) $ in Thousands			3 Months Ended		6 Months Ended
	Jun. 30, 2019	Dec. 31, 2018	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Property and Equipment [Line Items]
Capitalized internal-use software, gross	$ 123,700	$ 122,000	$ 123,700		$ 123,700
Capitalized internal-use software, net	23,900	26,500	23,900		23,900
Depreciation and amortization			59,944	$ 51,676	118,975	$ 101,615
Accrued capital expenditures	$ 24,900	$ 4,000
Property and Equipment [Member]
Property and Equipment [Line Items]
Depreciation and amortization			$ 55,300	$ 46,300	$ 109,500	$ 91,300