Accrued Liabilities (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Detail of accrued liabilities
Accrued vacation and employee-related expenses	$ 61,362	$ 35,803
Accrued incentives	57,585	46,554
Accrued sales tax and value-added taxes	8,536	9,103
Exercise of unvested stock options	498	1,292
Other accrued expenses	11,917	11,325
Total	$ 139,898	$ 104,077