Property and Equipment, Net (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Property and Equipment [Line Items]
Capitalized internal-use software, gross	$ 108,900		$ 108,900		$ 107,800
Capitalized internal-use software, net	26,800		26,800		$ 30,900
Depreciation and amortization	45,379	$ 40,657	88,282	$ 79,664
Property and Equipment [Member]
Property and Equipment [Line Items]
Depreciation and amortization	$ 40,500	$ 35,400	$ 79,200	$ 69,100