Significant accounting policies Other intangible assets with definite lives (Details) - USD ($)	Jan. 31, 2018	Jan. 31, 2017
Acquired Finite-Lived Intangible Assets [Line Items]
Patents, gross	$ 2,639,000	$ 2,627,000
Patents, accumulated amortization	2,426,000	$ 2,381,000
Patents, amortization expense, next twelve months	38,000
Patents, amortization expense, year two	35,100
Patents, amortization expense, year three	28,300
Patents, amortization expense, year four	17,500
Patents, amortization expense, year five	13,800
Patents, amortization expense, after year five	$ 80,211