Significant accounting policies Other intangible assets with definite lives (Details) - USD ($)	Jan. 31, 2016	Jan. 31, 2015
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-Lived Patents, Gross	$ 2,600,000	$ 2,700,000
Finite-Lived Intangible Assets, Accumulated Amortization	2,330,000	$ 2,280,000
Finite-Lived Intangible Assets, Amortization Expense, Next Twelve Months	42,900
Finite-Lived Intangible Assets, Amortization Expense, Year Two	39,900
Finite-Lived Intangible Assets, Amortization Expense, Year Three	30,900
Finite-Lived Intangible Assets, Amortization Expense, Year Four	27,900
Finite-Lived Intangible Assets, Amortization Expense, Year Five	21,700
Finite-Lived Intangible Assets, Amortization Expense, after Year Five	$ 88,207