Equity Method Investments (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Schedule Of Equity Method Investments [Line Items]
Distributions of income from unconsolidated affiliates	$ 1,250	$ 1,000
Equity Method Investments	$ 3,639		$ 4,022
Venture Fuels Partnership
Schedule Of Equity Method Investments [Line Items]
Equity investment in Venture Fuels Partnership (as a percent)	50.00%
Distributions of income from unconsolidated affiliates	$ 1,300	$ 1,000
Equity Method Investments	2,651		3,040
Other Investment [Member]
Schedule Of Equity Method Investments [Line Items]
Equity Method Investments	$ 988		$ 982