Accrued Liabilities (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Detail of accrued liabilities
Accrued vacation and employee-related expenses	$ 47,645	$ 35,803
Accrued incentives	20,325	46,554
Accrued sales tax and value-added taxes	8,701	9,103
Exercise of unvested stock options	1,017	1,292
Other accrued expenses	11,286	11,325
Total	$ 88,974	$ 104,077