Note 6 - Long-term Debt (Details Textual)		9 Months Ended
	May. 16, 2014 USD ($)	Sep. 30, 2015 USD ($)	Dec. 31, 2014 USD ($)
Line of Credit [Member]
Line of Credit Facility, Maximum Borrowing Capacity	$ 30,000,000
Minimum [Member]
Line of Credit Facility, Fixed Charge Coverage Ratio Covenant		1.25
Line of Credit Facility, Interest Rate During Period		2.17%
Maximum [Member]
Line of Credit Facility, Leverage Ratio Covenant		3.75
Line of Credit Facility, Interest Rate During Period		4.25%
Credit Facility Syndication, Number of Commercial Banks	11
Line of Credit Facility, Stated Borrowing Period	5 years
Line of Credit Facility, Maximum Borrowing Capacity Without Borrowing Base Requirement	$ 500,000,000
Line of Credit Facility, Accordion Feature, Additional Revolving Credit Commitments Under Existing Loan Facility	$ 100,000,000
Long-term Debt, Excluding Current Maturities		$ 332,155,000	$ 350,052,000
Letters of Credit Outstanding, Amount		3,700,000
Line of Credit Facility, Remaining Borrowing Capacity		164,100,000
Line of Credit Facility, Current Borrowing Capacity		$ 110,100,000