Derivative Instruments and Hedging Activities (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended					6 Months Ended				3 Months Ended		6 Months Ended
	Oct. 31, 2012 Interest expense [Member]	Oct. 31, 2011 Interest expense [Member]	Oct. 31, 2012 Interest expense [Member]	Oct. 31, 2011 Interest expense [Member]	Oct. 31, 2012 Interest rate swaps [Member]	Apr. 30, 2012 Interest rate swaps [Member]	Oct. 31, 2011 Interest rate swaps [Member]	Oct. 31, 2012 Interest rate swaps [Member] March 2012 Interest rate swap (variable rate loans) [Member]	Oct. 31, 2012 Interest rate swaps [Member] August 2010 Interest rate swap (variable rate loans) [Member]	Oct. 31, 2012 Forward exchange contracts [Member]	Oct. 31, 2011 Forward exchange contracts [Member]	Oct. 31, 2012 Forward exchange contracts [Member] Foreign exchange transaction losses [Member]	Oct. 31, 2011 Forward exchange contracts [Member] Foreign exchange transaction losses [Member]	Oct. 31, 2012 Forward exchange contracts [Member] Foreign exchange transaction losses [Member]	Oct. 31, 2011 Forward exchange contracts [Member] Foreign exchange transaction losses [Member]	Oct. 31, 2012 Fair value, fair value disclosure [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Variable rate loans outstanding																$ 701.9
Derivative [Line Items]
Interest rate swap agreements designated as fully effective cash flow hedges at end of period					2		1
Inception date								Mar. 30, 2012	Aug. 19, 2010
Fixed interest rate (in hundredths)								0.645%	0.80%
Fair value of derivative instrument					1.9	1.7	0.7			0.7	(0.2)
Basis of variable interest rate, reference rate reset period (in months)								1	1
Term Of Derivative Instrument								3 years	29 months
Expiration date								Mar. 31, 2015	Jan. 19, 2013
Notional amount of derivative liability								250.0	125.0	71.4	66.2
Debt Instrument, Description of Variable Rate Basis								one-month LIBOR	one-month LIBOR
Deferred Loss On Interest Rate Swap recorded as Other Accrued Liabilities					0.2	0.5
Deferred Loss On Interest Rate Swap Recorded As Other Long Term Liabilities					1.7	1.2	0.7
Derivative Instruments, Gain (Loss) [Line Items]
Net losses reclassified from Accumulated Other Comprehensive Loss	0.5	0.2	0.9	0.4
(Losses)/gains recognized on derivative instruments												$ 0.7	$ (0.5)	$ 0.6	$ (0.2)