Accrued Liabilities (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Detail of accrued liabilities
Accrued vacation and employee-related expenses	$ 47,600	$ 35,803
Accrued incentives	36,461	46,554
Accrued sales tax and value-added taxes	9,726	9,103
Exercise of unvested stock options	717	1,292
Other accrued expenses	11,614	11,325
Total	$ 106,118	$ 104,077