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, 2017	Jan. 31, 2016	Jan. 31, 2015	Jan. 31, 2017	Jan. 31, 2016	Jan. 31, 2015
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), before Tax [Roll Forward]
Net actuarial loss				$ 2,699	$ 2,504	$ 6,309
Prior service cost				(732)	(892)	0
Total pre-tax accumulated other comprehensive loss	$ 1,612	$ 6,309	$ 2,918	$ 1,967	$ 1,612	$ 6,309
Pre-tax accumulated other comprehensive loss - beginning of year related to benefit obligation	1,612	6,309	2,918
Recognized net (loss)	(146)	(261)	(152)
Amortization of prior service cost	160	66	0
Amendments	0	(958)	0
Net actuarial loss (gain)	341	(3,544)	3,543
Pre-tax accumulated other comprehensive loss - end of year related to benefit obligation	$ 1,967	$ 1,612	$ 6,309