Long-Term Debt (Details) - USD ($) $ in Millions		4 Months Ended	9 Months Ended	15 Months Ended
	Jul. 21, 2016	Jul. 21, 2016	Apr. 30, 2020	Mar. 14, 2016	Apr. 30, 2017	Mar. 15, 2016	Dec. 03, 2014
Line of Credit Facility [Line Items]
Maturity date		Mar. 15, 2021
Scenario 3
Line of Credit Facility [Line Items]
Long-term Debt			not to exceed $50.0 million
Scenario 4
Line of Credit Facility [Line Items]
Long-term Debt			not less than $75.0 million
Credit Agreement | Term Loan Facility
Line of Credit Facility [Line Items]
Maturity date		Dec. 03, 2019
Note Purchase Agreement | Senior Notes
Line of Credit Facility [Line Items]
Debt Instrument, Face Amount							$ 400.0
Note Purchase Agreement | Senior Notes, Series A
Line of Credit Facility [Line Items]
Debt instrument, interest rate							4.07%
Note Purchase Agreement | Senior Notes, Series B
Line of Credit Facility [Line Items]
Debt instrument, interest rate							4.19%
Note Purchase Agreement | Senior Notes, Series C
Line of Credit Facility [Line Items]
Debt instrument, interest rate							4.25%
Note Purchase Agreement | Senior Notes, Series D
Line of Credit Facility [Line Items]
Debt instrument, interest rate							4.35%
Senior Notes, Series A [Member] | Senior Notes
Line of Credit Facility [Line Items]
Debt Instrument, Face Amount							$ 100.0
Senior Notes, Series B [Member] | Senior Notes
Line of Credit Facility [Line Items]
Debt Instrument, Face Amount							100.0
Senior Notes, Series C [Member] | Senior Notes
Line of Credit Facility [Line Items]
Debt Instrument, Face Amount							100.0
Senior Notes, Series D [Member] | Senior Notes
Line of Credit Facility [Line Items]
Debt Instrument, Face Amount							100.0
Wells Fargo and Bank of America, N.A. | Line of Credit
Line of Credit Facility [Line Items]
Repayments of Lines of Credit	$ 242.5
Wells Fargo and Bank of America, N.A. | Revolving Credit Facility | Line of Credit | Minimum
Line of Credit Facility [Line Items]
Line of Credit Facility, Commitment Fee Percentage		0.15%
Wells Fargo and Bank of America, N.A. | Revolving Credit Facility | Line of Credit | Maximum
Line of Credit Facility [Line Items]
Line of Credit Facility, Commitment Fee Percentage		0.30%
Wells Fargo and Bank of America, N.A. | Term Loan Facility | Line of Credit
Line of Credit Facility [Line Items]
Quarterly amortization for term loan		$ 7.5
Wells Fargo and Bank of America, N.A. | Credit Agreement | Revolving Credit Facility
Line of Credit Facility [Line Items]
Maximum borrowing capacity							300.0
Wells Fargo and Bank of America, N.A. | Credit Agreement | Term Loan Facility
Line of Credit Facility [Line Items]
Maximum borrowing capacity							$ 300.0
Wells Fargo and Bank of America, N.A. | Credit Agreement | Term Loan Facility | Line of Credit
Line of Credit Facility [Line Items]
Quarterly amortization for term loan				$ 18.8
Wells Fargo and Bank of America, N.A. | First Amendment To Credit Agreement | Revolving Credit Facility
Line of Credit Facility [Line Items]
Maximum borrowing capacity						$ 350.0
Line of Credit, Maximum Borrowing Capacity, Increase						50.0
Wells Fargo and Bank of America, N.A. | First Amendment To Credit Agreement | Term Loan Facility
Line of Credit Facility [Line Items]
Maximum borrowing capacity						93.8
Outstanding borrowings						$ 93.8
Wells Fargo and Bank of America, N.A. | London Interbank Offered Rate (LIBOR), Adjusted LIBOR One | Minimum
Line of Credit Facility [Line Items]
Applicable interest rate added to reference rate in order to compute variable interest rate		0.125%
Wells Fargo and Bank of America, N.A. | London Interbank Offered Rate (LIBOR), Adjusted LIBOR One | Maximum
Line of Credit Facility [Line Items]
Applicable interest rate added to reference rate in order to compute variable interest rate		1.00%
Wells Fargo and Bank of America, N.A. | London Interbank Offered Rate (LIBOR), Adjusted LIBOR Two | Revolving Credit Facility | Minimum
Line of Credit Facility [Line Items]
Applicable interest rate added to reference rate in order to compute variable interest rate		1.125%
Wells Fargo and Bank of America, N.A. | London Interbank Offered Rate (LIBOR), Adjusted LIBOR Two | Revolving Credit Facility | Maximum
Line of Credit Facility [Line Items]
Applicable interest rate added to reference rate in order to compute variable interest rate		2.00%
WellsFargo,NationalAssociation,SunTrustBankandBankofAmerica,N.A.
Line of Credit Facility [Line Items]
Maturity date			Jul. 21, 2021
WellsFargo,NationalAssociation,SunTrustBankandBankofAmerica,N.A. | Revolving Credit Facility | Minimum
Line of Credit Facility [Line Items]
Line of Credit Facility, Commitment Fee Percentage			0.125%
WellsFargo,NationalAssociation,SunTrustBankandBankofAmerica,N.A. | Revolving Credit Facility | Maximum
Line of Credit Facility [Line Items]
Line of Credit Facility, Commitment Fee Percentage			0.20%
WellsFargo,NationalAssociation,SunTrustBankandBankofAmerica,N.A. | Revolving Credit Facility | Line of Credit
Line of Credit Facility [Line Items]
Outstanding borrowings			$ 0.0
WellsFargo,NationalAssociation,SunTrustBankandBankofAmerica,N.A. | Scenario 3
Line of Credit Facility [Line Items]
Line of Credit Facility, Covenant Terms			not to exceed $50.0 million
WellsFargo,NationalAssociation,SunTrustBankandBankofAmerica,N.A. | Scenario 4
Line of Credit Facility [Line Items]
Line of Credit Facility, Covenant Terms			not less than $75.0 million
WellsFargo,NationalAssociation,SunTrustBankandBankofAmerica,N.A. | Credit Agreement | Term Loan Facility
Line of Credit Facility [Line Items]
LIBOR variable interest rate			LIBOR Rate of 0.33% plus an applicable margin of 1.00%.
WellsFargo,NationalAssociation,SunTrustBankandBankofAmerica,N.A. | Second Amendment To Credit Agreement | Revolving Credit Facility
Line of Credit Facility [Line Items]
Maximum borrowing capacity	$ 500.0	$ 500.0			$ 850.0
WellsFargo,NationalAssociation,SunTrustBankandBankofAmerica,N.A. | Federal Funds Effective Swap Rate | Credit Agreement | Revolving Credit Facility
Line of Credit Facility [Line Items]
Applicable interest rate added to reference rate in order to compute variable interest rate			0.50%
WellsFargo,NationalAssociation,SunTrustBankandBankofAmerica,N.A. | London Interbank Offered Rate (LIBOR) | Credit Agreement | Revolving Credit Facility
Line of Credit Facility [Line Items]
Applicable interest rate added to reference rate in order to compute variable interest rate			1.00%
WellsFargo,NationalAssociation,SunTrustBankandBankofAmerica,N.A. | London Interbank Offered Rate (LIBOR), Adjusted LIBOR One | Revolving Credit Facility | Minimum
Line of Credit Facility [Line Items]
Applicable interest rate added to reference rate in order to compute variable interest rate			0.00%
WellsFargo,NationalAssociation,SunTrustBankandBankofAmerica,N.A. | London Interbank Offered Rate (LIBOR), Adjusted LIBOR One | Revolving Credit Facility | Maximum
Line of Credit Facility [Line Items]
Applicable interest rate added to reference rate in order to compute variable interest rate			0.75%
WellsFargo,NationalAssociation,SunTrustBankandBankofAmerica,N.A. | London Interbank Offered Rate (LIBOR), Adjusted LIBOR Two | Revolving Credit Facility | Minimum
Line of Credit Facility [Line Items]
Applicable interest rate added to reference rate in order to compute variable interest rate			1.00%
WellsFargo,NationalAssociation,SunTrustBankandBankofAmerica,N.A. | London Interbank Offered Rate (LIBOR), Adjusted LIBOR Two | Revolving Credit Facility | Maximum
Line of Credit Facility [Line Items]
Applicable interest rate added to reference rate in order to compute variable interest rate			1.75%