Retirement plans Cash flows (Details) $ in Thousands	12 Months Ended
	Jan. 31, 2018 USD ($)
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, contributions by employer	$ 0
Defined Benefit Plan, Benefit Obligation, Contributions by Plan Participant	0
Defined Benefit Plan, Expected Future Benefit Payment, Next Twelve Months	349
Defined Benefit Plan, Expected Future Benefit Payment, Year Two	348
Defined Benefit Plan, Expected Future Benefit Payment, Year Three	342
Defined Benefit Plan, Expected Future Benefit Payment, Year Four	347
Defined Benefit Plan, Expected Future Benefit Payment, Year Five	347
Defined Benefit Plan, Expected Future Benefit Payment, Five Fiscal Years Thereafter	$ 1,737