Note 3 - Long-Term Debt (Details Textual)	3 Months Ended						0 Months Ended	12 Months Ended			24 Months Ended	48 Months Ended	120 Months Ended	0 Months Ended	3 Months Ended				0 Months Ended		3 Months Ended			0 Months Ended	3 Months Ended
	Mar. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Mar. 31, 2015 Senior Note Due 2022 [Member] USD ($)	Dec. 31, 2014 Senior Note Due 2022 [Member] USD ($)	Dec. 05, 2012 Senior Note Due 2022 [Member] USD ($)	Mar. 12, 2012 Senior Note Due 2022 [Member] USD ($)	Mar. 14, 2017 Senior Note Due 2022 [Member] Scenario, Forecast [Member]	Mar. 14, 2020 Senior Note Due 2022 [Member] Scenario, Forecast [Member]	Mar. 14, 2019 Senior Note Due 2022 [Member] Scenario, Forecast [Member]	Mar. 14, 2018 Senior Note Due 2022 [Member] Scenario, Forecast [Member]	Mar. 12, 2022 Senior Note Due 2022 [Member] Scenario, Forecast [Member]	Mar. 14, 2017 Senior Note Due 2022 [Member] Scenario, Forecast [Member]	Mar. 12, 2022 Senior Note Due 2022 [Member] Scenario, Forecast [Member] USD ($)	Feb. 16, 2015 Multicurrency Credit Facility [Member] USD ($)	Mar. 31, 2015 Multicurrency Credit Facility [Member] USD ($)	Dec. 31, 2014 Multicurrency Credit Facility [Member] USD ($)	Sep. 26, 2014 Multicurrency Credit Facility [Member] USD ($)	Feb. 26, 2013 Multicurrency Credit Facility [Member] USD ($)	Feb. 16, 2015 Multicurrency Credit Facility [Member] Increased Unused Commitment Fee Rate [Member]	Feb. 16, 2015 Norwegian Facility [Member] USD ($)	Mar. 31, 2015 Norwegian Facility [Member] USD ($)	Mar. 31, 2015 Norwegian Facility [Member] NOK	Jun. 20, 2013 Norwegian Facility [Member] USD ($)	Feb. 16, 2015 Norwegian Facility [Member] Increased Unused Commitment Fee Rate [Member]	Mar. 31, 2015 Old Facility [Member] USD ($)	Mar. 31, 2015 Old Facility [Member] Senior Notes 775 [Member] USD ($)
Debt Instrument, Face Amount					$ 200,000,000	$ 300,000,000																600,000,000	$ 74,000,000			$ 160,000,000
Debt Instrument, Interest Rate, Stated Percentage						6.375%																				7.75%
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%
Debt Issuance Cost													12,700,000		4,900,000						1,300,000
Gains (Losses) on Extinguishment of Debt																									(4,200,000)
Long-term Debt, Fair Value			391,300,000
Long-term Debt, Gross	560,000,000	544,000,000	500,700,000	500,000,000											60,000,000	44,000,000
Line of Credit Facility, Maximum Borrowing Capacity	400,000,000																	150,000,000
Line of Credit Facility, Current Borrowing Capacity																	300,000,000
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage	0.375%													0.50%					0.125%	0.625%	0.50%			0.125%
Line of Credit Facility, Commitment Fee Amount														1,000,000						200,000
Long-term Debt	$ 560,000,000														$ 60,000,000
Debt, Weighted Average Interest Rate															2.44%