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		6 Months Ended
	Jul. 31, 2013	Jul. 31, 2012	Jul. 31, 2013	Jul. 31, 2012
Segment Reporting [Abstract]
Earnings from operations for segments	$ 206,998	$ 187,597	$ 389,960	$ 352,032
Unallocated corporate expenses	(30,112)	(33,017)	(62,537)	(62,467)
Interest and other expenses, net	(14,694)	(14,250)	(27,406)	(24,804)
Other operating expense	0	0	(9,379)	0
Earnings from operations before income taxes	$ 162,192	$ 140,330	$ 290,638	$ 264,761