Annual report pursuant to Section 13 and 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) (Recurring, USD $)
Dec. 31, 2012
Dec. 31, 2011
Fair Value, Inputs, Level 2 | Interest Rate Swap
   
Liabilities, Fair Value Disclosure [Abstract]    
Interest rate swap instruments $ 8,214,582 $ 6,711,961
Fair Value, Inputs, Level 3
   
Liabilities, Fair Value Disclosure [Abstract]    
Contingent consideration 1,147,408 2,734,464
Fair Value
   
Liabilities, Fair Value Disclosure [Abstract]    
Total $ 9,361,990 $ 9,446,425