Employee Retirement Benefits - The accumulated benefit obligation (Details) (Other Postretirement Benefit Plan, Defined Benefit [Member], USD $) In Thousands, unless otherwise specified	12 Months Ended
	Jan. 31, 2015	Jan. 31, 2014	Jan. 31, 2013
Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Beginning liability balance	$ 8,254	$ 8,307	$ 7,560
Service cost	195	202	187
Interest cost	366	348	335
Actuarial (gain) loss and assumption changes	3,543	(340)	433
Retiree benefits paid	(233)	(263)	(208)
Ending liability balance	$ 12,125	$ 8,254	$ 8,307