Note 15 - Long-term Debt (Details Textual) $ / shares in Units, $ in Thousands, shares in Millions							1 Months Ended	12 Months Ended
	Mar. 26, 2020 USD ($)	Mar. 25, 2020	Oct. 29, 2019 USD ($) $ / shares	Jul. 29, 2019 USD ($)	Nov. 15, 2018 USD ($)	May 14, 2018 USD ($)	Nov. 30, 2019 USD ($) $ / shares	Dec. 31, 2019 USD ($) $ / shares shares	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Jun. 14, 2018 USD ($)	May 31, 2018 USD ($)	Mar. 31, 2018 USD ($)
Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months								$ 8,400
Long-term Debt, Maturities, Repayments of Principal in Year Two								8,500
Long-term Debt, Maturities, Repayments of Principal in Year Three								8,500
Long-term Debt, Maturities, Repayments of Principal in Year Four								142,300
Long-term Debt, Maturities, Repayments of Principal in Year Five								231,100
Long-term Debt, Maturities, Repayments of Principal after Year Five								7,900
Long-term Debt, Current Maturities, Total								8,244	$ 47,286		$ 8,263	$ 48,397	$ 47,281	$ 116,796	$ 207,982			$ 47,298
Repayments of Long-term Debt, Total								313,150	153,924	$ 45,000
Long-term Debt, Excluding Current Maturities, Total								356,108	335,119		$ 394,841	$ 366,896	$ 333,290	$ 316,926	$ 280,710			$ 176,011
Long-term Debt, Gross								193,700
Payments for Equity Derivative Instrument, Net of Fees								$ 37,375	(0)	(0)
Share Price, Potential Dilutive Effect (in dollars per share) | $ / shares								$ 31.47
Proceeds from Issuance of Warrants								$ 11,500	0	0
Debt Conversion, Converted Instrument, Amount								$ 0	53,086	$ 0
Adjustments To Additional Paid In Capital Premium On Convertible Notes									30,702
Warrants Issued With 2.75% Convertible Notes [Member]
Share Price, Potential Dilutive Effect (in dollars per share) | $ / shares			$ 53.44
Proceeds from Issuance of Warrants			$ 11,200
London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument, Basis Spread on Variable Rate								2.76%
The 2.75% Convertible Notes [Member]
Debt Instrument, Convertible, Carrying Amount of Equity Component							$ 27,900	$ 36,300
Debt Instrument, Face Amount							$ 230,000
Debt Instrument, Interest Rate, Stated Percentage							2.75%	2.75%
Debt Instrument, Interest Rate, Effective Percentage							6.62%	6.62%
Debt Instrument, Convertible, Conversion Ratio							31.7776
Debt Instrument, Convertible, Conversion Price (in dollars per share) | $ / shares							$ 31.47
Debt Instrument, Convertible, Sale Price to Conversion Price, Percentage							130.00%
Debt Instrument, Redemption Price, Percentage Occurence of Fundamental Change							100.00%
Long-term Debt, Gross							$ 192,600
Debt Instrument, Convertible, Carrying Amount of Equity Component, Tax Amount			9,500				9,500
Payments for Equity Derivative Instrument, Net of Fees			$ 27,900
Share Price, Potential Dilutive Effect (in dollars per share) | $ / shares			$ 31.47
Debt Instrument, Unamortized Discount, Total							37,400
Debt Issuance Costs, Net, Total							$ 6,400	$ 5,400
Debt Instrument, Unamortized Discount, Reclassified From Equity								1,100
Third Party Offering Costs, Equity Component								1,000
The 2019 Notes [Member] | Senior Notes [Member]
Debt Instrument, Face Amount									$ 40,000
Debt Instrument, Interest Rate, Stated Percentage									6.11%
Long-term Debt, Current Maturities, Total									$ 40,000
Repayments of Long-term Debt, Total				$ 40,000
The Credit Agreement [Member]
Line of Credit Facility, Maximum Borrowing Capacity																	$ 200,000
Line of Credit, Covenant, Minimum Cash Balance																	150,000
Debt Instrument, Covenant, Minimum Acquisition Cash Consideration for Leverage Ratio																	100,000
Letters of Credit Outstanding, Amount								$ 31,900
Consolidated Leverage Ratio, Actual								1.72
Consolidated Interest Coverage Ratio, Actual								10.95
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								2.00%
Debt Instrument, Interest Rate, Effective Percentage								3.91%
The Credit Agreement [Member] | Base Rate [Member]
Debt Instrument, Basis Spread on Variable Rate								1.00%
Debt Instrument, Interest Rate, Effective Percentage								5.75%
The Credit Agreement [Member] | Revolving Credit Facility [Member]
Line of Credit Facility, Maximum Borrowing Capacity																	350,000
Line of Credit Facility, Remaining Borrowing Capacity								$ 293,100
Long-term Line of Credit, Total								25,000	197,000
The Credit Agreement [Member] | Term Loan [Member]
Debt Instrument, Face Amount																	$ 150,000
Long-term Debt, Current Maturities, Total								7,500	7,500
Debt Instrument, Periodic Payment, Principal Balance Percentage																	1.25%
Long-term Debt, Excluding Current Maturities, Total								131,300	$ 138,800
The Credit Agreement [Member] | Line of Credit [Member] | Revolving Credit Facility [Member] | Subsequent Event [Member]
Line of Credit Facility, Maximum Borrowing Capacity	$ 275,000
The Credit Agreement [Member] | Line of Credit [Member] | Revolving Credit Facility [Member] | Subsequent Event [Member] | London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument, Basis Spread on Variable Rate	3.00%	2.00%
The 4.25% Convertible Notes [Member]
Debt Instrument, Interest Rate, Stated Percentage																4.25%
Debt Instrument, Fair Value Disclosure, Total																$ 69,900
Debt Conversion, Converted Instrument, Amount						$ 500
Debt Instrument, Cash Settlements						$ 300
Debt Instrument, Increase, Accrued Interest					$ 1,500
8% Convertible Notes [Member]
Debt Instrument, Interest Rate, Stated Percentage									8.00%							8.00%
Debt Instrument, Fair Value Disclosure, Total																$ 121,600
Debt Conversion, Converted Instrument, Amount								$ 52,000
Adjustments To Additional Paid In Capital Premium On Convertible Notes									$ 30,700
Debt Conversion, Converted Instrument, Shares Issued (in shares) | shares								1.2
Repayments of Convertible Debt								$ 38,900
Interest Paid, Including Capitalized Interest, Operating and Investing Activities, Total								$ 900