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, 2016	Jan. 31, 2015	Jan. 31, 2014	Jan. 31, 2016	Jan. 31, 2015	Jan. 31, 2014
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), before Tax [Roll Forward]
Net actuarial loss				$ 2,504	$ 6,309	$ 2,918
Prior service cost				(892)	0	0
Total pre-tax accumulated other comprehensive loss	$ 6,309	$ 2,918	$ 3,441	$ 1,612	$ 6,309	$ 2,918
Pre-tax accumulated other comprehensive loss - beginning of year related to benefit obligation	6,309	2,918	3,441
Recognized net (loss)	(261)	(152)	(183)
Amortization of prior service cost	66	0	0
Amendments	(958)	0	0
Net actuarial (gain) loss	(3,544)	3,543	(340)
Pre-tax accumulated other comprehensive loss - end of year related to benefit obligation	$ 1,612	$ 6,309	$ 2,918