Debt (Narrative) (Details) (USD $)	0 Months Ended
	May 31, 2012	Jan. 12, 2011	Apr. 30, 2013
Line of Credit Facility [Line Items]
Line of credit facility, initiation date		Jan. 12, 2011
Required minimum Interest coverage ratio	3.00
Required maximum total leverage ratio	3.75
Interest Coverage Ratio			48.54
Total Leverage Ratio			0.66
Amount available under the credit agreement			$ 710,000,000
Write-off debt issuance costs in interest expense	1,400,000
Existing debt issuance costs	6,000,000
Debt issuance costs incurred to refinance Credit Agreement	1,300,000
Minimum [Member]
Line of Credit Facility [Line Items]
Commitment fee percentage	0.10%
Line of credit facility interest rate margin on base rate loans percentage	0.00%
Line of credit facility interest rate margin on foreign currency loans percentage	1.00%
Maximum [Member]
Line of Credit Facility [Line Items]
Commitment fee percentage	0.275%
Line of credit facility interest rate margin on base rate loans percentage	0.75%
Line of credit facility interest rate margin on foreign currency loans percentage	1.75%
Revolving Credit Facilities [Member]
Line of Credit Facility [Line Items]
Aggregate commitment amount of credit facilities		1,000,000,000
Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Additional borrowings	$ 500,000,000
Expiration date	May 31, 2017