Income taxes Income taxes (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jul. 31, 2017	Jul. 31, 2016	Jul. 31, 2017	Jul. 31, 2016
Income Tax Disclosure [Abstract]
effective income tax rate from continuing operations	24.90%	47.10%	16.80%	15.30%
Unrecognized tax benefits	$ 200,000		$ 200,000
Unrecognized tax benefits, income tax penalties and interest expense	1,200
Unrecognized tax benefits, income tax penalties and interest accrued	$ 47,900		$ 47,900
Income Tax Contingency [Line Items]
Income Tax Examination, Description			The Internal Revenue Service ("IRS") began an audit of the fiscal year ended January 31, 2015 in August 2016. In August 2017, the Company received a notice from the IRS that it had concluded the tax audit for the year ended January 31, 2015. No changes were made to the reported tax.