Employee Retirement Benefits The components of net periodic benefit cost for postretirement benefits (Details) (Other Postretirement Benefit Plans, Defined Benefit [Member], USD $) In Thousands, unless otherwise specified	3 Months Ended
	Apr. 30, 2012	Apr. 30, 2011
Other Postretirement Benefit Plans, Defined Benefit [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Service cost	$ 47	$ 30
Interest cost	84	84
Amortization of actuarial losses	58	32
Net periodic benefit cost	$ 189	$ 146