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Segment Reporting and Geographic Information (Details)
3 Months Ended 9 Months Ended
Sep. 30, 2012
Sep. 30, 2011
Sep. 30, 2012
Sep. 30, 2011
Revenue by geographic region        
Revenue by geographic region 100.00% 100.00% 100.00% 100.00%
United States [Member]
       
Revenue by geographic region        
Revenue by geographic region 93.00% 95.00% 94.00% 94.00%
Canada [Member]
       
Revenue by geographic region        
Revenue by geographic region 7.00% 5.00% 6.00% 5.00%
Other countries [Member] | Maximum [Member]
       
Revenue by geographic region        
Revenue by geographic region 1.00% 1.00% 1.00% 1.00%