Property and Equipment, Net (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Property and Equipment [Line Items]
Capitalized internal-use software, gross	$ 97,400		$ 97,400		$ 92,700
Capitalized internal-use software, net	34,800		34,800		$ 33,600
Depreciation and amortization	43,254	$ 36,755	85,852	$ 70,249
Property and Equipment [Member]
Property and Equipment [Line Items]
Depreciation and amortization	$ 36,000	$ 30,900	$ 71,300	$ 59,800