Quarterly report pursuant to Section 13 or 15(d)

Fair Value Measurement - Fair Value of Liabilities Measured on a Recurring Basis (Details)

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Fair Value Measurement - Fair Value of Liabilities Measured on a Recurring Basis (Details) (Fair Value, Measurements, Recurring [Member], USD $)
Sep. 30, 2012
Dec. 31, 2011
Fair Value, Inputs, Level 2 [Member] | Interest Rate Swap [Member]
   
Liabilities, Fair Value Disclosure [Abstract]    
Derivative instruments $ 7,152,044 $ 6,711,961
Fair Value, Inputs, Level 3 [Member]
   
Liabilities, Fair Value Disclosure [Abstract]    
Contingent consideration 2,766,994 2,734,464
Estimate of Fair Value, Fair Value Disclosure [Member]
   
Liabilities, Fair Value Disclosure [Abstract]    
Total liabilities $ 9,919,038 $ 9,446,425