Quarterly report pursuant to Section 13 or 15(d)

Summary of Significant Accounting Policies - Business Segment (Details)

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Summary of Significant Accounting Policies - Business Segment (Details) (USD $)
3 Months Ended 6 Months Ended
Jun. 30, 2012
Jun. 30, 2011
Jun. 30, 2012
segment
region
Jun. 30, 2011
Segment Reporting Information [Line Items]        
Number of reportable segments     4  
Number of U.S. regions reported in aggregate     4  
Income before taxes and unallocated corporate expenses $ 4,874,909 $ 3,298,358 $ 8,891,275 $ 7,369,541
Unallocated Amount to Segment [Member]
       
Segment Reporting Information [Line Items]        
Indirect expenses 9,996,615 8,681,007 22,654,749 18,377,185
All Other [Member]
       
Segment Reporting Information [Line Items]        
Number of U.S. regions reported in aggregate     4  
Income before taxes and unallocated corporate expenses $ 4,874,909 $ 3,298,358 $ 8,891,275 $ 7,369,541