Note 6 - Long-term Debt (Details Textual)	6 Months Ended
	Jun. 30, 2015 USD ($)	Dec. 31, 2014 USD ($)	May. 16, 2014 USD ($)
Letter 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, 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	$ 360,000,000	$ 350,052,000
Letters of Credit Outstanding, Amount	3,700,000
Line of Credit Facility, Remaining Borrowing Capacity	136,300,000
Line of Credit Facility, Current Borrowing Capacity	$ 87,500,000