Floating Rate Debentures, 6.25% Debentures, and 4.00% Debentures had been Dilutive Included Additional Income and Additional Incremental Common Shares (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Jan. 31, 2010 Floating Rate Debentures due 2023	Jan. 31, 2011 6.25% Debentures	Jan. 31, 2010 6.25% Debentures	Jan. 31, 2012 4.00% Debentures due 2031
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Additional income	$ 633	$ 3,062	$ 2,643	$ 2,075
Additional incremental common shares	1,415