ESPP (Details)	12 Months Ended
	Dec. 31, 2012
Employee Stock Purchase Plan description	90% of the lesser of the average market price of a share on the first business day of the offering period or the average market price of a share on the last business day of the offering period of three months
Stock Issued During Period, Shares, Employee Stock Purchase Plans	2,300,000
Employee stock purchase plan
Maximum Employee Subscription Rate	10.00%
Maximum Number of Shares Per Employee	900
Number of shares initially available for grant	15,000,000