Employee Retirement Benefits The accumulated benefit obligation (Details) (Other Postretirement Benefit Plans, Defined Benefit [Member], USD $) In Thousands, unless otherwise specified	12 Months Ended
	Jan. 31, 2012	Jan. 31, 2011	Jan. 31, 2010
Other Postretirement Benefit Plans, Defined Benefit [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation at beginning of year	$ 5,969	$ 5,512	$ 4,840
Service cost	121	62	55
Interest cost	334	324	332
Actuarial (gain) loss and assumption changes	1,363	237	476
Total recognized in net and other comprehensive income	1,818	623	863
Retiree benefits paid	(227)	(166)	(191)
Benefit obligation at end of year	$ 7,560	$ 5,969	$ 5,512