Significant accounting policies Other intangible assets with definite lives (Details) (USD $)	Jan. 31, 2013	Jan. 31, 2012
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-Lived Patents, Gross	$ 2,600,000	$ 2,500,000
Finite-Lived Intangible Assets, Accumulated Amortization	2,180,000	2,200,000
Finite-Lived Intangible Assets, Amortization Expense, Next Twelve Months	49,200
Finite-Lived Intangible Assets, Amortization Expense, Year Two	44,600
Finite-Lived Intangible Assets, Amortization Expense, Year Three	41,400
Finite-Lived Intangible Assets, Amortization Expense, Year Four	37,500
Finite-Lived Intangible Assets, Amortization Expense, Year Five	34,400
Finite-Lived Intangible Assets, Amortization Expense, after Year Five	$ 165,600