Long-Term Debt Narrative (Details)	May 31, 2018 USD ($)	Jun. 30, 2018 USD ($)
Debt Instrument [Line Items]
Deferred debt issuance costs, current		$ 400,000
Deferred debt issuance costs, noncurrent		1,700,000
Revolving credit facility with interest at a variable rate (June 30, 2018 - 3.3%; December 30, 2017 - 2.7%)
Debt Instrument [Line Items]
Long-term line of credit outstanding		197,000,000
Line of credit maximum borrowing capacity		$ 450,000,000
Ratio of interest coverage to earnings for the last four fiscal quarters		4.0
Ratio of leverage to earnings for the last four fiscal quarters		3.5
Private Placement
Debt Instrument [Line Items]
Deferred debt issuance costs, current	$ 100,000
Deferred debt issuance costs, noncurrent	600,000
Borrowings	100,000,000
Seven-year fixed rate notes with an interest rate of 4.22%
Debt Instrument [Line Items]
Borrowings	$ 50,000,000
Note term	7 years
Stated Interest Rate Percentage	4.22%
Ten-year fixed rate notes with an interest rate of 4.40%
Debt Instrument [Line Items]
Borrowings	$ 50,000,000
Note term	10 years
Stated Interest Rate Percentage	4.40%

Debt Instrument, Covenant, Ratio of Interest Coverage to Earnings for the Last Four Fiscal Quarters

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- Definition

Debt Instrument, Covenant, Ratio of Leverage to Earnings for the Last Four Fiscal Quarters

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Face (par) amount of debt instrument at time of issuance.

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
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Contractual interest rate for funds borrowed, under the debt agreement.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Period of time between issuance and maturity of debt instrument, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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- Definition

Amount, before accumulated amortization, of debt issuance costs classified as current. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

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Amount, before accumulated amortization, of debt issuance costs classified as noncurrent. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

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The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

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Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

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