Long-Term and Short-Term Financing Arrangements (Narrative) (Details) - USD ($) $ in Thousands					3 Months Ended
	Aug. 26, 2015	Jul. 27, 2015	Jul. 24, 2015	Dec. 18, 2014	Apr. 30, 2016	May. 11, 2011
Debt Instrument [Line Items]
Line of Credit Facility, Expiration Date				Dec. 18, 2019
Line of Credit Facility, Maximum Borrowing Capacity				$ 600,000
Line Of Credit Borrowing Capacity Increase Option				$ 150,000
Line Of Credit Facility Percentage Of Borrowing Base Under Condition One				12.50%
Number of consecutive business days for borrowing base availability over minimum under condition one				30 days
Line Of Credit Facility Percentage Of Borrowing Base Under Condition Two				10.00%
Line Of Credit Facility Borrowing Base Availability Under Condition Two				$ 50,000
Line of Credit, Current					$ 0
Letters of Credit Outstanding, Amount					6,500
Line of Credit Facility, Remaining Borrowing Capacity					$ 485,500
Two Thousand Nineteen Senior Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount						$ 200,000
Debt Instrument, Interest Rate, Stated Percentage						7.125%
Principal Amount Redeemed in Tender Offer	$ 39,300		$ 160,700
Debt Instrument, Redemption Price, Percentage	103.563%		103.95%
Two Thousand Twenty Three Senior Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount		$ 200,000
Debt Instrument, Interest Rate, Stated Percentage		6.25%
Debt Instrument, Redemption Price, Percentage					101.00%
Proceeds from Issuance of Debt		$ 196,300
Debt Instrument, Maturity Date		Aug. 15, 2023