Employee Benefit Plans (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Oct. 31, 2011	Oct. 31, 2010	Oct. 31, 2011	Oct. 31, 2010
Pension Benefits [Member]
Net periodic pension and other postretirement benefit expense
Service cost	$ 3,386	$ 3,061	$ 10,568	$ 9,604
Interest cost	6,508	5,909	18,989	17,904
Expected return on plan assets	(4,339)	(4,266)	(14,036)	(13,176)
Amortization of prior service cost	265	270	798	808
Amortization of net loss	2,626	644	5,353	2,164
Net expense	8,446	5,618	21,672	17,304
Other Postretirement Benefits [Member]
Net periodic pension and other postretirement benefit expense
Service cost	642	590	1,649	1,284
Interest cost	821	816	2,326	2,208
Amortization of prior service cost	(164)	(164)	(494)	(494)
Amortization of net loss	6	1	12	1
Net expense	$ 1,305	$ 1,243	$ 3,493	$ 2,999