Note I - Long-term Debt (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Nov. 05, 2014	May 16, 2014
Note I - Long-term Debt (Details) [Line Items]
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
Debt Issuance Cost	1,200,000
Long-term Debt, Excluding Current Maturities	350,052,000	40,000,000
Letters of Credit Outstanding, Amount	4,400,000	3,000,000
Line of Credit Facility, Remaining Borrowing Capacity	145,500,000
Line of Credit Facility, Current Borrowing Capacity	140,100,000
Deferred Finance Costs, Net	5,800,000	4,600,000
Accumulated Amortization, Deferred Finance Costs	3,500,000	3,100,000
Amortization of Financing Costs	500,000	500,000	600,000
Previous Agreement [Member]
Note I - Long-term Debt (Details) [Line Items]
Line of Credit Facility, Expiration Date	Mar. 14, 2017
Amended Agreement [Member]
Note I - Long-term Debt (Details) [Line Items]
Line of Credit Facility, Expiration Date	May 16, 2019
Line Of Credit Facility, Maximum Borrowing Capacity Without Borrowing Base Requirement					400,000,000
Line of Credit Facility, Accordion Feature, Additional Revolving Credit Commitments Under Existing Loan Facility					100,000,000
Letter of Credit [Member]
Note I - Long-term Debt (Details) [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity				$ 30,000,000
Minimum [Member]
Note I - Long-term Debt (Details) [Line Items]
Line Of Credit Facility, Fixed Charge Coverage Ratio, Covenant	1.25
Line of Credit Facility, Interest Rate During Period	1.40%
Maximum [Member]
Note I - Long-term Debt (Details) [Line Items]
Line Of Credit Facility, Leverage Ratio Covenant	3.75
Line of Credit Facility, Interest Rate During Period	4.25%