Employee Retirement Benefits - Pre-tax adjustment to accumulated benefit obligation (Details) - Other Postretirement Benefit Plan, Defined Benefit - USD ($) $ in Thousands	12 Months Ended
	Jan. 31, 2020	Jan. 31, 2019	Jan. 31, 2020	Jan. 31, 2019
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), before Tax [Roll Forward]
Net actuarial loss			$ 3,070	$ 2,114
Prior service cost			(253)	(413)
Total pre-tax accumulated other comprehensive loss	$ 1,701	$ 1,701	2,817	$ 1,701
Pre-tax accumulated other comprehensive loss - beginning of year related to benefit obligation	1,701	2,142
Recognized net (loss)	(97)	(128)
Amortization of prior service cost	160	160
Net actuarial (gain) loss	1,053	(473)
Pre-tax accumulated other comprehensive loss - end of year related to benefit obligation	$ 2,817	$ 1,701
Expected postretirement medical and other benefit payments in fiscal 2020			$ 337