The Company and basis of presentation (Details Textual)	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Concentration Risk, Percentage	10.00%	10.00%	10.00%	10.00%
Accounts Receivable [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Concentration Risk, Percentage			10.00%		10.10%
Supplier Concentration Risk [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Concentration Risk, Percentage	12.00%	10.00%	13.30%	10.00%
Hong Kong Highpower Technology Company Limited [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Equity Method Investment, Ownership Percentage	100.00%		100.00%