Summary of Significant Accounting Policies - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jan. 01, 2018
Schedule of Equity Method Investments [Line Items]
Reserves for potential refund	$ 0	$ 0
Allowance for doubtful accounts	0	0
Asset impairments	0	0	$ 0
Asset retirement obligation	0	6,600,000
Accretion expense		200,000	200,000
Clean-up costs incurred	$ 100,000	$ 400,000	$ 100,000
Potentially dilutive units outstanding (in units)	0	0
Accounting Standards Update 2014-09
Schedule of Equity Method Investments [Line Items]
Cumulative effect transition adjustment resulting from earlier recognition of revenue				$ (2,300,000)
Explorer
Schedule of Equity Method Investments [Line Items]
Ownership	12.62%	2.62%
State of Washington Department of Ecology
Schedule of Equity Method Investments [Line Items]
Environmental accrual	$ 300,000	$ 300,000
Difference between Revenue Guidance in Effect before and after Topic 606 | Accounting Standards Update 2014-09
Schedule of Equity Method Investments [Line Items]
Cumulative effect transition adjustment resulting from earlier recognition of revenue				4,600,000
Difference between Revenue Guidance in Effect before and after Topic 606 | Mars Oil Pipeline Company LLC (“Mars”) | Accounting Standards Update 2014-09
Schedule of Equity Method Investments [Line Items]
Cumulative effect transition adjustment resulting from earlier recognition of revenue				$ (6,900,000)