Note 6 - Equity Method Investments and Joint Ventures Equity Method Investments, Narrative (Details)	Dec. 31, 2018
Rangeland RIO Pipeline, LLC [Member]
Equity Method Investment, Ownership Percentage	67.00%
Minnesota Pipe Line Company, LLC [Member]
Equity Method Investment, Ownership Percentage	17.00%
PNAC [Member]
Equity Method Investment, Ownership Percentage	50.00%
Rendezvous Gas Services, L.L.C.
Equity Method Investment, Ownership Percentage	78.00%
Three Rivers Gathering, LLC
Equity Method Investment, Ownership Percentage	50.00%
Uintah Basin Field Services, LLC
Equity Method Investment, Ownership Percentage	38.00%