Share Based Compensation (Details) (USD $)	3 Months Ended		9 Months Ended		0 Months Ended			9 Months Ended	0 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended
	Oct. 31, 2013	Oct. 31, 2012	Oct. 31, 2013	Oct. 31, 2012	Mar. 25, 2013 2010 Stock Incentive Plan [Member]	Aug. 27, 2012 2010 Stock Incentive Plan [Member]	Apr. 02, 2012 2010 Stock Incentive Plan [Member]	Oct. 31, 2013 2010 Stock Incentive Plan [Member]	Mar. 25, 2013 Time-vested RSUs [Member] 2010 Stock Incentive Plan [Member]	Apr. 02, 2012 Time-vested RSUs [Member] 2010 Stock Incentive Plan [Member]	Oct. 31, 2013 Time-vested RSUs [Member] 2010 Stock Incentive Plan [Member]	Oct. 31, 2012 Time-vested RSUs [Member] 2010 Stock Incentive Plan [Member]	Oct. 31, 2013 Time-vested RSUs [Member] 2010 Stock Incentive Plan [Member]	Oct. 31, 2012 Time-vested RSUs [Member] 2010 Stock Incentive Plan [Member]	Oct. 31, 2013 Performance-based RSUs [Member] 2010 Stock Incentive Plan [Member]	Oct. 31, 2012 Performance-based RSUs [Member] 2010 Stock Incentive Plan [Member]	Oct. 31, 2013 Performance-based RSUs [Member] 2010 Stock Incentive Plan [Member]	Oct. 31, 2012 Performance-based RSUs [Member] 2010 Stock Incentive Plan [Member]	Oct. 31, 2013 Performance-based RSUs [Member] 2010 Stock Incentive Plan [Member] Minimum [Member]	Oct. 31, 2013 Performance-based RSUs [Member] 2010 Stock Incentive Plan [Member] Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grants in period (in shares)	0	7,600			198,900	7,600	151,200				0	0			0	0
Stock options vesting period, years								4 years					3 years				3 years
Years to expiration								5 years
Weighted average grant date fair value (in dollars per share)			$ 9.34	$ 10.92									$ 32.85	$ 31.66			$ 32.85	$ 31.66
Grants in period (in shares)									25,540	21,120							56,222	50,940
Perfromance shares target award																			0.00%	150.00%
Number of shares granted based on target award percentage																	100.00%