Lease obligations (Details) (USD $)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Lease obligations
Lease obligations of US for 2015			$ 89,150
Lease obligations of US for 2016		90,710
Lease obligations of US for 2017	7,559
Total lease obligations of US			187,419
Lease obligations of HK for 2015			48,000
Lease obligations of HK for 2016		6,000
Total lease obligations of HK			54,000
Lease obligations of US and HK for 2015			137,150
Lease obligations of US and HK for 2016		96,710
Lease obligations of US and HK for 2017	7,559
Total lease obligations of US and HK			$ 240,419