Segment Information - Reconciliation of Segments' Earnings from Operations to Company's Consolidated Earnings from Operations Before Income Taxes (Detail) (USD $)	3 Months Ended		6 Months Ended
	Jul. 31, 2014	Jul. 31, 2013	Jul. 31, 2014	Jul. 31, 2013
Segment Reporting [Abstract]
Earnings from operations for segments	$ 241,983,000	$ 206,998,000	$ 486,040,000	$ 389,960,000
Unallocated corporate expenses	(33,462,000)	(30,112,000)	(67,726,000)	(62,537,000)
Interest and other expenses, net	(16,151,000)	(14,694,000)	(32,427,000)	(27,406,000)
Other operating expense	0	0	0	(9,379,000)
Earnings from operations before income taxes	$ 192,370,000	$ 162,192,000	$ 385,887,000	$ 290,638,000