Employee Benefit Plans (Details) (USD $) In Thousands	3 Months Ended		6 Months Ended
	Jul. 31, 2011	Jul. 31, 2010	Jul. 31, 2011	Jul. 31, 2010
Pension Benefits [Member]
Net periodic pension and other postretirement benefit expense
Service cost	$ 3,592	$ 3,274	$ 7,182	$ 6,543
Interest cost	6,274	5,998	12,481	11,995
Expected return on plan assets	(4,849)	(4,455)	(9,697)	(8,910)
Amortization of prior service cost	267	269	533	538
Amortization of net loss	1,404	760	2,727	1,520
Net expense	6,688	5,846	13,226	11,686
Other Postretirement Benefits [Member]
Net periodic pension and other postretirement benefit expense
Service cost	504	347	1,007	694
Interest cost	753	696	1,505	1,392
Amortization of prior service cost	(165)	(165)	(330)	(330)
Amortization of net loss	3		6
Net expense	$ 1,095	$ 878	$ 2,188	$ 1,756