Employee Benefit Plans - Schedule of Net Periodic Pension and Other Postretirement Benefit Expense (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Oct. 31, 2013	Oct. 31, 2012	Oct. 31, 2013	Oct. 31, 2012
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 4,783	$ 4,528	$ 14,360	$ 13,566
Interest cost	6,752	6,701	20,256	20,099
Expected return on plan assets	(5,560)	(5,104)	(16,680)	(15,312)
Amortization of prior service cost	243	254	729	762
Amortization of net loss	4,753	3,949	14,258	11,927
Net expense	10,971	10,328	32,923	31,042
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	698	596	2,094	1,787
Interest cost	691	710	2,072	2,130
Expected return on plan assets	0	0	0	0
Amortization of prior service cost	(165)	(165)	(495)	(495)
Amortization of net loss	53	7	159	22
Net expense	$ 1,277	$ 1,148	$ 3,830	$ 3,444