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, 2014	Jan. 31, 2013	Jan. 31, 2012
Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Beginning liability balance	$ 8,307	$ 7,560	$ 5,969
Service cost	202	187	121
Interest cost	348	335	334
Actuarial (gain) loss and assumption changes	(340)	433	1,363
Retiree benefits paid	(263)	(208)	(227)
Ending liability balance	$ 8,254	$ 8,307	$ 7,560