Summary of Significant Accounting Policies - Additional Information (Details)	12 Months Ended
	Dec. 31, 2017 USD ($) renewal_option shares	Dec. 31, 2016 USD ($) shares	Dec. 31, 2015 USD ($)	Jan. 01, 2018 USD ($)	Nov. 30, 2017
Schedule of Equity Method Investments [Line Items]
Reserves for potential refund	$ 0	$ 0
Deferred revenue, current	19,400,000	13,900,000
Allowance for doubtful accounts	0	0
Asset impairments	0	0	$ 0
Asset retirement obligation	6,600,000	6,400,000
Accretion expense	200,000	200,000	200,000
Clean-up costs incurred	400,000	100,000	$ 100,000
Clean-up costs accrued	300,000	6,800,000
Environmental accrual	$ 0	$ 6,300,000
Potentially dilutive units outstanding (in units) | shares	0	0
Explorer
Schedule of Equity Method Investments [Line Items]
Ownership	12.62%	12.62%			2.62%
State of Washington Department of Ecology
Schedule of Equity Method Investments [Line Items]
Environmental accrual	$ 300,000	$ 500,000
Portland Harbor Superfund Site
Schedule of Equity Method Investments [Line Items]
Environmental accrual		$ 6,300,000
Option to Extend for Two Additional Five Year Terms
Schedule of Equity Method Investments [Line Items]
Lease revenue related party agreements, term	10 years
Lease revenue related party agreements, option of renewal | renewal_option	2
Lease revenue related party agreements, renewal term	5 years
Option to Extend for Ten Additional One Year Terms
Schedule of Equity Method Investments [Line Items]
Lease revenue related party agreements, term	10 years
Lease revenue related party agreements, option of renewal | renewal_option	10
Lease revenue related party agreements, renewal term	1 year
Difference between Revenue Guidance in Effect before and after Topic 606 | Accounting Standards Update 2014-09 | Scenario, Forecast
Schedule of Equity Method Investments [Line Items]
Cumulative effect transition adjustment resulting from earlier recognition of revenue				$ 4,500,000
Difference between Revenue Guidance in Effect before and after Topic 606 | Mars Oil Pipeline Company LLC (“Mars”) | Accounting Standards Update 2014-09 | Scenario, Forecast
Schedule of Equity Method Investments [Line Items]
Cumulative effect transition adjustment resulting from earlier recognition of revenue				$ 9,600,000