Cost of revenues and general and administrative expenses (Details 1) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
General and administrative expenses	$ 14,542,817	$ 13,651,650	$ 11,329,648
Employee Costs [Member]
General and administrative expenses	5,751,142	5,265,360	4,219,915
Insurance [Member]
General and administrative expenses	968,662	965,003	951,715
Professional Fees [Member]
General and administrative expenses	2,097,294	3,112,678	2,805,146
Director's Fees and Expenses [Member]
General and administrative expenses	608,429	551,132	519,786
Depreciation [Member]
General and administrative expenses	421,851	252,303	340,969
Other Credit Derivatives [Member]
General and administrative expenses	$ 4,695,439	$ 3,505,174	$ 2,492,117