Employee Retirement Benefits - Pre-tax adjustment to accumulated benefit obligation (Details) - Other Postretirement Benefit Plan, Defined Benefit [Member] - USD ($) $ in Thousands	12 Months Ended
	Jan. 31, 2018	Jan. 31, 2017	Jan. 31, 2018	Jan. 31, 2017
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), before Tax [Roll Forward]
Net actuarial loss			$ 2,714	$ 2,699
Prior service cost			(572)	(732)
Total pre-tax accumulated other comprehensive loss	$ 2,142	$ 1,967	$ 2,142	$ 1,967
Pre-tax accumulated other comprehensive loss - beginning of year related to benefit obligation	1,967	1,612
Recognized net (loss)	(96)	(146)
Amortization of prior service cost	159	160
Net actuarial loss (gain)	112	341
Pre-tax accumulated other comprehensive loss - end of year related to benefit obligation	$ 2,142	$ 1,967