Note 7 - Intangible Assets, Net (Tables)

12 Months Ended

Dec. 31, 2019

Notes Tables

Schedule of Finite-Lived Intangible Assets [Table Text Block]

	As of December 31,
	2018			2019
	(in thousands)
Customer relationships	$	19,214		$	19,214
Deferred charges related to pipeline connection agreements		2,716			2,653
Intangible assets, gross		21,930			21,867
Accumulated amortization of intangible assets		(5,096	)		(7,779	)
Intangible assets, net	$	16,834		$	14,088

Schedule of Finite-Lived Intangible Assets, Future Amortization Expense [Table Text Block]

For year ending:
December 31, 2020	$	2,746
December 31, 2021		2,746
December 31, 2022		2,746
December 31, 2023		1,321
December 31, 2024		1,321
Thereafter		3,208
Total estimated aggregate amortization expense	$	14,088