Note 1 - Significant Accounting Policies (Details Textual) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Restricted Cash, Total	$ 0	$ 0
Capitalized Interest Costs, Including Allowance for Funds Used During Construction, Total	1,911	6,686	$ 6,033
Impairment of Long-Lived Assets Held-for-use	$ 0	$ 0	$ 0
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized (in shares)	2,600,000
Preferred Stock, Shares Authorized (in shares)	500,000
Preferred Stock, Shares Issued, Total (in shares)	0
Preferred Stock, Shares Outstanding, Ending Balance (in shares)	0
Common Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized (in shares)	2,300,000