Income taxes (Details 3) (USD $)	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Deferred tax assets:
Net operating loss carry-forwards	$ 27,188,180	$ 26,186,094
Stock options	3,514,890	3,312,860
Bonuses and salaries	33,111	279,424
Restricted stock	73,538
Provision for doubtful accounts	13,703	492,002
Foreign nonrefundable withholding tax	318,163
Other	22,937	159,225
Total deferred tax assets	31,164,522	30,429,605
Less: Valuation allowance	(29,416,464)	(29,238,264)
Net deferred tax assets	1,748,058	1,191,341
Deferred tax liabilities:
Depreciation and amortization	(981,816)	(1,008,449)
Total deferred tax liabilities	(981,816)	(1,008,449)
Total deferred tax assets, net	$ 766,242	$ 182,892	$ 0