Property and Equipment, Net (Narrative) (Details) - USD ($) $ in Thousands			3 Months Ended		9 Months Ended
	Sep. 30, 2019	Dec. 31, 2018	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Property and Equipment [Line Items]
Capitalized internal-use software, gross	$ 126,900	$ 122,000	$ 126,900		$ 126,900
Capitalized internal-use software, net	25,100	26,500	25,100		25,100
Depreciation and amortization			55,196	$ 54,863	174,171	$ 156,478
Accrued capital expenditures	$ 8,000	$ 4,000
Property and Equipment [Member]
Property and Equipment [Line Items]
Depreciation and amortization			$ 50,500	$ 49,700	$ 160,000	$ 141,000