Transactions with Related Parties (Narrative) (Details) - Affiliated Entity - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Poseidon Oil Pipeline Company
Related Party Transaction [Line Items]
Net sales from related party	$ 12,902	$ 12,669	$ 12,557	[1]
Due from related parties	2,600	2,400
Costs charged by related party, included in operating costs	960	975	994	[1]
Poseidon Oil Pipeline Company | Asset Management Arrangement
Related Party Transaction [Line Items]
Net sales from related party	9,200	8,900	8,600
ANSAC
Related Party Transaction [Line Items]
Net sales from related party	236,408	367,133	373,606
Due from related parties	43,400	68,075
Costs charged by related party, included in operating costs	$ 2,460	$ 4,446	$ 5,284

[1] We own a 64% interest in Poseidon Oil Pipeline Company, LLC.