Employee Retirement Benefits - The liability and expense reflected in the balance sheet and income statement (Details) - USD ($) $ in Thousands	12 Months Ended
	Jan. 31, 2018	Jan. 31, 2017
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Long-term portion in other liabilities	$ 8,264	$ 8,054
Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation at beginning of year	8,416	7,991
Net periodic benefit cost	323	399
Other comprehensive loss	175	355
Total recognized in net periodic benefit cost and other comprehensive income	498	754
Retiree benefits paid	343	329
Benefit obligation at end of year	8,571	8,416
Current portion in accrued liabilities	307	362
Long-term portion in other liabilities	$ 8,264	$ 8,054
Assumptions used to calculate benefit obligation:
Discount rate	3.75%	4.00%
Rate of compensation increase	4.00%	4.00%
Health care cost trend rate assumed for next year	6.50%	6.67%
Ultimate health care cost trend rate	4.50%	4.50%
Year that the rate reaches the ultimate trend rate	2030	2030
Assumptions used to calculated the net periodic benefit cost:
Discount rate	4.00%	4.25%
Rate of compensation increase	4.00%	4.00%
Defined Benefit Plan, Effect of One-Percentage Point Change in Assumed Health Care Cost Trend Rates
Effect on total of service and interest cost components, one percentage point increase	$ 71
Effect on total of service and interest cost components, one percentage point decrease	(58)
Effect on accumulated postretirement benefit obligation, one percentage point increase	1,180
Effect on accumulated postretirement benefit obligation, one percentage point decrease	(1,045)
2019	313
2020	323
2021	332
2022	341
2023-2028	$ 2,192