Represents the discount rate for debt instrument issued.

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Percentage of fronting fee to each issuing bank annually on the average dollar amount of any outstanding letters of credit.

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The percentage of required participation fee on the letter of credit.

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Represents the underwriting discount on senior notes.

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Amount equal to the present value (the principal) at the beginning of the lease term of minimum lease payments during the lease term (excluding that portion of the payments representing executory costs such as insurance, maintenance, and taxes to be paid by the lessor, together with any profit thereon) net of payments or other amounts applied to the principal through the balance sheet date.

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Amount of capital lease obligation due within one year or the normal operating cycle, if longer.

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Amount of minimum lease payments for capital leases.

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Amount necessary to reduce net minimum lease payments to present value for capital leases.

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

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Contractual interest rate for funds borrowed, under the debt agreement.

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Percentage price of original principal amount of debt at which debt can be redeemed by the issuer.

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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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Amount, after accumulated amortization, of debt discount.

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Amount of interest capitalized during the period.

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Amount of the cost of borrowed funds accounted for as interest expense for debt.

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The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

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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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Amount of cash outflow for pension benefit. Includes, but is not limited to, employer contribution to fund plan asset and payment to retiree. Excludes other postretirement benefit.

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The cash inflow from a borrowing with the highest claim on the assets of the entity in case of bankruptcy or liquidation (with maturities initially due after one year or beyond the operating cycle, if longer).

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Note 9 - Debt, Credit Facilities and Capital Leases (Details Textual) $ in Millions			3 Months Ended		12 Months Ended
	May 31, 2016 USD ($)	Apr. 12, 2013 USD ($)	Mar. 31, 2018 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2014 USD ($)	Mar. 05, 2018 USD ($)	Mar. 05, 2018 CAD ($)	Dec. 31, 2017 USD ($)
Letters of Credit Outstanding, Amount			$ 2,600,000
Capital Lease Obligations, Total			12,764,000					$ 11,800,000
Capital Lease Obligations, Current			5,669,000					5,608,000
Capital Lease Obligations, Noncurrent			7,094,000					6,193,000
Capital Leases, Future Minimum Payments Due, Total			13,590,000
Capital Leases, Future Minimum Payments, Interest Included in Payments			826,000
Revolving Credit Facility [Member]
Line of Credit Facility, Maximum Borrowing Capacity	$ 100,000,000
Debt Instrument, Term	3 years
Long-term Line of Credit, Total			0					$ 0
Letter of Credit [Member]
Letter of Credit Outstanding, Fronting Fee	0.20%
Letter of Credit [Member] \| Minimum [Member]
Letter of Credit, Participation Fee, Percent	2.25%
Letter of Credit [Member] \| Maximum [Member]
Letter of Credit, Participation Fee, Percent	3.25%
Senior Notes [Member]
Debt Instrument, Face Amount		$ 500,000,000
Payment for Pension Benefits					$ 6,500,000
Proceeds from Issuance of Senior Long-term Debt		$ 490,000,000
Underwriting Discount on Senior Notes		2.00%
Debt Instrument, Unamortized Discount, Total		$ 10,000,000	4,000,000
Debt Instrument, Interest Rate, Stated Percentage		6.875%
Interest Expense, Debt, Total			$ 9,100,000	$ 8,100,000
Interest Costs Capitalized				$ 900,000
Debt Instrument, Redemption Price, Percentage			101.00%
Series 2018-A Senior Notes [Member]
Debt Instrument, Face Amount						$ 30,800,000	$ 40.0
Debt Instrument, Unamortized Discount, Total							$ 0.2
Debt Instrument, Interest Rate, Stated Percentage						4.68%	4.68%
Interest Expense, Debt, Total			$ 400,000
Debt Instrument, Issuance, Discount Rate						0.58%	0.58%