Fair value measurements (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Sep. 30, 2015
Fair value measurements
Warrant liability - related party	$ 976	$ 117
Derivative liability		488
Recurring
Fair value measurements
Cash and cash equivalents	2,588	4,077
Trade accounts receivable	380	546
Short-term investments	334	72
Assets	3,302	4,695
Warrant liability	922	93
Warrant liability - related party	976	117
Derivative liability		488
Liabilities	$ 1,898	$ 698
Fair value Assumptions
Company's ending stock price (in dollars per share)	$ 0.58	$ 0.20
Company's stock volatility (as a percent)	110.00%	85.00%
Risk free interest rate (as a percent)	1.39%	1.48%
Recurring | Level 1
Fair value measurements
Cash and cash equivalents	$ 2,588	$ 4,077
Trade accounts receivable	380	546
Short-term investments	334	72
Assets	3,302	4,695
Recurring | Level 3
Fair value measurements
Warrant liability	922	93
Warrant liability - related party	976	117
Derivative liability		488
Liabilities	$ 1,898	$ 698
Non-recurring
Fair value measurements
Mineral properties			$ 1,354
Assets			1,354
Non-recurring | Level 3
Fair value measurements
Mineral properties			1,354
Assets			$ 1,354