Segment Information - Reconciliation of Segments' Earnings from Operations to Company's Consolidated Earnings from Operations Before Income Taxes (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
Segment Reporting [Abstract]
Earnings from operations for segments	$ 184,115	$ 147,916	$ 574,075	$ 499,948
Unallocated corporate expenses	(30,497)	(30,621)	(93,034)	(93,088)
Interest and other expenses, net	(13,922)	(14,783)	(41,328)	(39,587)
Other operating expense	0	0	(9,379)	0
Earnings from operations before income taxes	$ 139,696	$ 102,512	$ 430,334	$ 367,273