Accrued Liabilities (Details) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Accrued Liabilities [Abstract]
Accrued payroll taxes and other employee-related expenses	$ 71,678	$ 75,881
Accrued incentives	64,437	96,708
Other accrued expenses	41,104	44,987
Accrued commissions	39,246	65,794
Accrued sales tax and value-added taxes	23,894	23,681
Accrued vacation	13,419	9,741
Total	$ 253,778	$ 316,792