Property and Equipment, Net (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Property and Equipment [Line Items]
Capitalized internal-use software, gross	$ 108,000		$ 107,800
Capitalized internal-use software, net	28,500		$ 30,900
Depreciation and amortization	42,904	$ 39,008
Property and Equipment [Member]
Property and Equipment [Line Items]
Depreciation and amortization	$ 38,800	$ 33,700