Share Based Compensation Outstanding stock options (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
	Jan. 31, 2012 Y
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Outstanding, January 31, 2011	445
Outstanding, January 31, 2011, Weighted average exercise price	$ 33.86
Granted, Number of options	136
Granted, Weighted average exercise price	$ 59.99
Exercised, Number of options	(84)
Exercised, Weighted average exercise price	$ 29.74
Forfeited, Number of options	(1)
Forfeited, Weighted average exercise price	$ 28.01
Outstanding, January 31, 2012	496
Outstanding, January 31, 2012, Weighted average exercise price	$ 41.73
Outstanding, January 31, 2012, Aggregate intrinsic value	$ 11,474
Outstanding, January 31, 2012, Weighted average remaining contractual term (years)	3.27
Exercisable, January 31, 2012, Number of options	181
Exercisable, January 31, 2012, Weighted average exercis price	$ 32.04
Exercisable, January 31, 2012, Aggregate intrinsic value	$ 5,956
Exercisable, January 31, 2012, Weighted average remaining contractual term (years)	2.16