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, 2021	Jan. 31, 2020	Jan. 31, 2021	Jan. 31, 2020
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), before Tax [Roll Forward]
Net actuarial loss			$ 2,817	$ 3,070
Prior service cost			290	(253)
Total pre-tax accumulated other comprehensive loss	$ 3,107	$ 1,701	3,107	$ 2,817
Pre-tax accumulated other comprehensive loss - beginning of year related to benefit obligation	2,817	1,701
Recognized net (loss)	(173)	(97)
Amortization of prior service cost	160	160
Net actuarial loss	303	1,053
Pre-tax accumulated other comprehensive loss - end of year related to benefit obligation	$ 3,107	$ 2,817
Expected postretirement medical and other benefit payments in fiscal 2022			$ 369