Note 7 - Intangibles and Other Assets, Net Other Assets - Net of Accumulated Depreciation (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Customer relationships	$ 19,214	$ 19,214
Deferred charges related to pipeline connection agreements	2,653	2,716
Intangible assets, gross	21,867	21,930
Accumulated amortization of intangible assets	(7,779)	(5,096)
Total estimated aggregate amortization expense	$ 14,088	$ 16,834