Note 4 - Long-term Debt (Details Textual) NOK in Billions				1 Months Ended	3 Months Ended	6 Months Ended	9 Months Ended	12 Months Ended			20 Months Ended	24 Months Ended
	Jul. 07, 2015 USD ($)	Jul. 07, 2015 USD ($)	Jul. 02, 2015 USD ($)	Feb. 16, 2015 USD ($)	Sep. 30, 2015 USD ($)	Jun. 30, 2015 USD ($)	Sep. 26, 2014 USD ($)	Mar. 14, 2020	Mar. 14, 2019	Mar. 14, 2018	Mar. 14, 2017	Mar. 12, 2022	Sep. 30, 2015 NOK	Sep. 30, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 05, 2012 USD ($)	Mar. 12, 2012 USD ($)
Norwegian Facility [Member]
Long-term Line of Credit														$ 0
Debt Instrument, Face Amount													NOK 0.6	70,400,000
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage		0.65%				0.50%
Line of Credit Facility, Commitment Fee Amount	$ 100,000			$ 200,000
Line of Credit Facility, Covenant, Minimum Liquidity	$ 50,000,000	$ 50,000,000
Debt Issuance Cost						$ 1,300,000
Multicurrency Credit Facility [Member] | London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument, Basis Spread on Variable Rate			2.75%
Multicurrency Credit Facility [Member]
Long-term Line of Credit														23,000,000
Long-term Debt, Gross														$ 23,000,000	$ 44,000,000
Line of Credit Facility, Current Borrowing Capacity							$ 300,000,000
Line of Credit Facility, Maximum Borrowing Capacity			$ 200,000,000				$ 400,000,000
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage			0.75%	0.50%			0.375%
Line of Credit Facility, Commitment Fee Amount				$ 1,000,000
Line of Credit Facility, Covenant, Minimum Liquidity			$ 50,000,000
Payments of Debt Restructuring Costs			$ 1,000,000
Interest Expense, Debt					$ 1,800,000
Debt Issuance Cost					$ 4,400,000
Debt, Weighted Average Interest Rate													2.95%	2.95%
Line of Credit Facility, Remaining Borrowing Capacity														$ 175,100,000
Senior Note Due 2022 [Member] | Scenario, Forecast [Member]
Redemption Price as Percentage of Principal Amount Premium and Interest								101.063%	102.125%	103.188%	100.00%	100.00%
Debt Instrument, Basis Spread on Variable Rate											0.50%
Senior Note Due 2022 [Member] | Deferred Costs and Other Assets [Member]
Unamortized Debt Issuance Expense														12,700,000
Senior Note Due 2022 [Member]
Debt Instrument, Face Amount																$ 200,000,000	$ 300,000,000
Debt Instrument, Interest Rate, Stated Percentage																	6.375%
Long-term Debt, Fair Value														306,300,000
Long-term Debt, Gross														500,600,000	500,000,000
Long-term Debt, Gross														$ 523,000,000	$ 544,000,000