Employee Benefit Plans - Schedule of Net Periodic Pension and Other Postretirement Benefit Expense (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jul. 31, 2013	Jul. 31, 2012	Jul. 31, 2013	Jul. 31, 2012
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 4,521	$ 4,622	$ 9,577	$ 9,038
Interest cost	6,639	6,811	13,504	13,398
Expected return on plan assets	(6,170)	(5,322)	(11,120)	(10,208)
Amortization of prior service cost	243	254	486	508
Amortization of net loss	4,305	3,988	9,505	7,978
Net expense	9,538	10,353	21,952	20,714
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	673	489	1,396	1,191
Interest cost	653	624	1,381	1,420
Expected return on plan assets	0	0	0	0
Amortization of prior service cost	(165)	(165)	(330)	(330)
Amortization of net loss	10	(81)	106	15
Net expense	$ 1,171	$ 867	$ 2,553	$ 2,296