Share Based Compensation (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended									6 Months Ended	3 Months Ended	6 Months Ended
	Jul. 31, 2012	Apr. 30, 2012	Jul. 31, 2011	Jul. 31, 2012 Time Vested Units [Member] 2010 Stock Incentive Plan [Member]	Apr. 30, 2012 Time Vested Units [Member] 2010 Stock Incentive Plan [Member]	Jul. 31, 2011 Time Vested Units [Member] 2010 Stock Incentive Plan [Member]	Jul. 31, 2012 Performance Based Restricted Stock Units [Member] 2010 Stock Incentive Plan [Member]	Apr. 30, 2012 Performance Based Restricted Stock Units [Member] 2010 Stock Incentive Plan [Member]	Jul. 31, 2011 Performance Based Restricted Stock Units [Member] 2010 Stock Incentive Plan [Member]	Jul. 31, 2011 Performance Based Restricted Stock Units [Member] 2010 Stock Incentive Plan [Member]	Apr. 30, 2012 Restricted Stock Units [Member] 2010 Stock Incentive Plan [Member]	Jul. 31, 2012 Minimum [Member] Performance Based Restricted Stock Units [Member] 2010 Stock Incentive Plan [Member]	Jul. 31, 2012 Maximum [Member] Performance Based Restricted Stock Units [Member] 2010 Stock Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted, number of options, in shares	0	151	0	0	21	0	0	51	0	0
Stock options vesting period, years		4 years			3 years			3 years
Years to expiration		5 years
Perfromance Shares Target Award												0.00%	150.00%
Weighted average grant date fair value		$ 10.96									$ 31.66