Share Based Compensation Outstanding stock units (Details) (Director [Member], USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
	Jan. 31, 2012
Director [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]
Outstanding, January 31, 2012, Number of units	27
Outstanding, January 31, 2011, Weighted average price	$ 47.24
Granted, Number of units	3
Granted, Weighted average price	$ 51.89
Deferred retainers, Number of units	1
Deferred retainers, Weighted average price	$ 51.89
Dividends, Number of units	1
Dividends, Weighted average price	$ 58.62
Converted into common shares, Number of units	(7)
Converted into common shares, Weighted average price	$ 56.82
Outstanding, January 31, 2012, Number of units	25
Outstanding, January 31, 2012, Weighted average price	$ 64.89