Accumulated other comprehensive income (loss) (Details) - USD ($)	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Marketable securities
Beginning balance		$ (12,563)
Gains (losses) on available for sale securities	$ 0
Less: Tax (tax benefit)		0
Net gains (losses) on available for sale securities	0
(Gains) Losses reclassified from accumulated other comprehensive income to net income		12,563
Less: Tax (tax benefit)	0
Net gains (losses) reclassified from accumulated other comprehensive income to net income		12,563
Other comprehensive income (loss), net of tax		$ 12,563
Ending balance	$ 0