Employee Benefit Plans (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Employee Benefit Plans
Percentage of employee's current contributions matched by employer	100.00%
Maximum percentage of employee's total eligible compensation that can be matched by employer	3.00%
Maximum amount of employee contributions that can be matched by employer per participant per year	$ 5,100
Employer matching contributions	6,000,000	5,500,000	3,400,000
Expenses related to retirement savings-related plans for foreign subsidiaries	$ 3,400,000	$ 3,600,000	$ 3,500,000