Income taxes (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Components of income (loss) before provision for income taxes by jurisdiction
United States	$ 2,563,036	$ 537,097	$ (6,307,445)
Outside United States	1,397,812	(474,222)	2,002,251
Income (loss) from operations before provision for income taxes	3,960,848	62,875	(4,305,194)
Current tax:
United States-State and local	9,456	5,754	11,056
Outside United States	756,752	619,043	417,837
Total current tax	766,208	624,797	428,893
Deferred tax:
Outside United States	34,255	(583,928)	(281,782)
Total deferred tax	34,255	(583,928)	(281,782)
Provision for income taxes, net	800,463	40,869	147,111
Amount of deferred tax asset from which it is more likely than not that the Company would realize the benefit	29,900,000	31,200,000	29,200,000
Valuation allowance	28,475,080	29,416,464	29,200,000
Deferred tax liability	653,074	981,816
Deferred tax liability/ net deferred tax asset	$ 727,495	$ 766,242	$ 200,000