Related party transactions (Details) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Related party transactions
Rent	$ 422,882	$ 500,785	$ 487,677
Consulting and professional fees	$ 56,986	$ 132,103	$ 74,246
BDP Realty Corporation
Related party transactions
Ownership interest owned by related party (as a percent)	33.30%