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, 2019	Jan. 31, 2018	Jan. 31, 2019	Jan. 31, 2018
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), before Tax [Roll Forward]
Net actuarial loss			$ 2,114	$ 2,714
Prior service cost			(413)	(572)
Total pre-tax accumulated other comprehensive loss	$ 1,701	$ 2,142	1,701	$ 2,142
Pre-tax accumulated other comprehensive loss - beginning of year related to benefit obligation	2,142	1,967
Recognized net (loss)	(128)	(96)
Amortization of prior service cost	160	159
Net actuarial (gain) loss	(473)	112
Pre-tax accumulated other comprehensive loss - end of year related to benefit obligation	$ 1,701	$ 2,142
Expected postretirement medical and other benefit payments in fiscal 2020			$ 330