Share Based Compensation (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended			9 Months Ended	3 Months Ended			9 Months Ended	3 Months Ended			9 Months Ended	3 Months Ended	9 Months Ended
	Oct. 31, 2012	Apr. 30, 2012	Oct. 31, 2011	Oct. 31, 2012	Oct. 31, 2012 Time Vested Units [Member] 2010 Stock Incentive Plan [Member]	Apr. 30, 2012 Time Vested Units [Member] 2010 Stock Incentive Plan [Member]	Oct. 31, 2011 Time Vested Units [Member] 2010 Stock Incentive Plan [Member]	Oct. 31, 2011 Time Vested Units [Member] 2010 Stock Incentive Plan [Member]	Oct. 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]	Oct. 31, 2011 Performance Based Restricted Stock Units [Member] 2010 Stock Incentive Plan [Member]	Oct. 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]	Oct. 31, 2012 Minimum [Member] Performance Based Restricted Stock Units [Member] 2010 Stock Incentive Plan [Member]	Oct. 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	8	151	0		0	21	0	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				$ 10.92									$ 31.66