Note 5 - Long-term Debt (Details Textual)	Jun. 30, 2016 USD ($)	Dec. 31, 2015 USD ($)	May 16, 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
Maximum [Member]
Line of Credit Facility, Leverage Ratio Covenant	3.75
Weighted Average [Member]
Long-term Debt, Weighted Average Interest Rate	2.46%
Credit Facility Syndication, Number of Commercial Banks			11
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	$ 317,904,000	$ 311,532,000
Letters of Credit Outstanding, Amount	3,600,000
Line of Credit Facility, Remaining Borrowing Capacity	178,500,000
Line of Credit Facility, Current Borrowing Capacity	$ 126,400,000