Note 13 - Long-term Debt and Credit Arrangements (Details Textual) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Long-term Debt, Current Maturities, Total	$ 8,700	$ 8,253	$ 8,278
Long-term Debt, Excluding Current Maturities, Total	$ 331,647	355,911	330,522
London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument, Basis Spread on Variable Rate	2.76%
The Credit Agreement [Member]
Consolidated Leverage Ratio, Actual	1.94
Consolidated Leverage Ratio, Covenant Maximum	3.00
Consolidated Interest Coverage Ratio, Actual	6.79
Debt Instrument, Covenant, Minimum Consolidated Interest Coverage Ratio	4.00
The Credit Agreement [Member] \| London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument, Basis Spread on Variable Rate	3.00%
Debt Instrument, Interest Rate, Effective Percentage	2.38%
The Credit Agreement [Member] \| Base Rate [Member]
Debt Instrument, Basis Spread on Variable Rate	2.00%
Debt Instrument, Interest Rate, Effective Percentage	3.88%
The Credit Agreement [Member] \| Revolving Credit Facility [Member]
Line of Credit Facility, Remaining Borrowing Capacity	$ 226,600
Letters of Credit Outstanding, Amount	48,400
Long-term Line of Credit, Total	0
The Credit Agreement [Member] \| Term Loan [Member]
Long-term Debt, Current Maturities, Total	7,500	7,500	7,500
Long-term Debt, Excluding Current Maturities, Total	$ 121,900	$ 129,400	$ 123,800
The 2.75% Convertible Notes [Member]
Debt Instrument, Interest Rate, Stated Percentage	2.75%	2.75%	2.75%
Long-term Debt, Gross	$ 202,000	$ 195,300	$ 200,300
Debt Instrument, Unamortized Discount, Total	28,000	34,700	$ 29,700
Interest Paid, Including Capitalized Interest, Operating and Investing Activities, Total	1,700	1,600
Amortization of Debt Discount (Premium)	$ 600	$ 900

The actual consolidated interest coverage ratio.

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The actual consolidated leverage ratio.

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The maximum consolidated leverage ratio allowed under the covenant terms.

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The minimum consolidated interest coverage ratio under the debt instrument agreement.

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No definition available.

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Amount of noncash expense included in interest expense to amortize debt discount and premium associated with the related debt instruments. Excludes amortization of financing costs. Alternate captions include noncash interest expense.

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Percentage points added to the reference rate to compute the variable rate on the debt instrument.

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No definition available.

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- Definition

Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

+ References

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- Definition

Effective interest rate for the funds borrowed under the debt agreement considering interest compounding and original issue discount or premium.

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

+ References

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Amount, after accumulated amortization, of debt discount.

+ References

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Amount of cash paid for interest, including, but not limited to, capitalized interest and payment to settle zero-coupon bond attributable to accreted interest of debt discount and debt instrument with insignificant coupon interest rate in relation to effective interest rate of borrowing attributable to accreted interest of debt discount; classified as operating and investing activities.

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- Definition

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

+ References

No definition available.

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- Definition

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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- Definition

Amount of borrowing capacity currently available under the credit facility (current borrowing capacity less the amount of borrowings outstanding).

+ References

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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt, classified as current. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ References

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Amount after unamortized (discount) premium and debt issuance costs of long-term debt classified as noncurrent and excluding amounts to be repaid within one year or the normal operating cycle, if longer. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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