Note 8 - Long-term Debt and Credit Facility (Details Textual) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Dec. 31, 2019	Mar. 12, 2018	Oct. 31, 2015
Long-term Debt, Total	$ 303,668	$ 278,520
Long-term Debt, Fair Value	294,000	286,900
Derivative, Fixed Interest Rate			2.937%
A 2015 Interest Rate Swap [Member]
Derivative Asset, Notional Amount				$ 262,500
Derivative, Fixed Interest Rate				1.46%
A 2018 Interest Rate Swap [Member]
Derivative Asset, Notional Amount			$ 170,600
Derivative, Fixed Interest Rate			2.937%
Derivative, Amount of Hedged Item			$ 170,600
Term Loan [Member]
Long-term Debt, Total	245,000	253,800
A 2015 Credit Facility [Member]
Debt Instrument, Face Amount				$ 650,000
Line of Credit Facility, Maximum Borrowing Capacity				350,000
Long-term Line of Credit, Total	58,000	24,000
Other Loans Payable, Total	700	$ 800
Letters of Credit Outstanding, Amount	$ 25,100
Derivative, Amount of Hedged Item				$ 262,500
Credit Facility Maximum Consolidated Leverage Ratio	3.25
Credit Facility Actual Consolidated Leverage Ratio	3.12
Line of Credit Facility, Remaining Borrowing Capacity	$ 12,700
Credit Facility Minimum Consolidated Fixed Charge Ratio	1.25
Credit Facility Actual Consolidated Fixed Charge Ratio	1.38
A 2015 Credit Facility [Member] | London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument, Interest Rate, Effective Percentage	3.11%
A 2015 Credit Facility [Member] | London Interbank Offered Rate (LIBOR) [Member] | Minimum [Member]
Debt Instrument, Basis Spread on Variable Rate	1.25%
A 2015 Credit Facility [Member] | London Interbank Offered Rate (LIBOR) [Member] | Maximum [Member]
Debt Instrument, Basis Spread on Variable Rate	2.25%
A 2015 Credit Facility [Member] | Term Loan [Member]
Debt Instrument, Face Amount	$ 308,400
Debt Instrument, Term (Year)	5 years
Debt Instrument, Interest Rate, Effective Percentage	3.71%
A 2015 Credit Facility [Member] | Revolving Credit Facility [Member]
Line of Credit Facility, Maximum Borrowing Capacity	$ 225,000
Debt Instrument, Term (Year)	5 years
Proceeds from (Repayments of) Debt, Total	$ 34,000
A 2015 Credit Facility [Member] | Insurance Carries Collateral [Member]
Letters of Credit Outstanding, Amount	12,200
A 2015 Credit Facility [Member] | Working Performance Obligation [Member]
Letters of Credit Outstanding, Amount	$ 12,900