Employee Retirement Benefits - The accumulated benefit obligation (Details) - Other Postretirement Benefit Plan, Defined Benefit	12 Months Ended
	Jan. 31, 2019 USD ($) basesppoints	Jan. 31, 2018 USD ($)
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation at beginning of year	$ 8,571,000	$ 8,416,000
Service cost	28,000	74,000
Interest cost	316,000	312,000
Actuarial (gain) loss and assumption changes	(473,000)	112,000
Retiree benefits paid	441,000	343,000
Benefit obligation at end of year	8,001,000	8,571,000
Plan assets on unfunded plan	$ 0	$ 0
Defined benefit plan change in discount rate | basesppoints	50