Significant accounting policies Other intangible assets with definite lives (Details) - USD ($)	Jan. 31, 2017	Jan. 31, 2016
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-Lived Patents, Gross	$ 2,600,000	$ 2,600,000
Finite-Lived Intangible Assets, Accumulated Amortization	2,400,000	$ 2,300,000
Finite-Lived Intangible Assets, Amortization Expense, Next Twelve Months	44,400
Finite-Lived Intangible Assets, Amortization Expense, Year Two	35,400
Finite-Lived Intangible Assets, Amortization Expense, Year Three	32,400
Finite-Lived Intangible Assets, Amortization Expense, Year Four	26,000
Finite-Lived Intangible Assets, Amortization Expense, Year Five	17,200
Finite-Lived Intangible Assets, Amortization Expense, after Year Five	$ 91,161