Investments in and Advances to Equity Accounted Investments - Schedule of Investments in and Advances to Equity Accounted Investments (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Schedule of Equity Method Investments [Line Items]
Investment in and advances to equity accounted investments	$ 25,170	$ 25,460
High-Q Joint Venture
Schedule of Equity Method Investments [Line Items]
Investment in and advances to equity accounted investments	25,170	24,546
Gemini Tankers L.L.C.
Schedule of Equity Method Investments [Line Items]
Investment in and advances to equity accounted investments	$ 0	$ 914

Total investments in (A) an entity in which the entity has significant influence, but does not have control, (B) subsidiaries that are not required to be consolidated and are accounted for using the equity and or cost method, and (C) an entity in which the reporting entity shares control of the entity with another party or group. Includes long-term advances receivable from a party that is affiliated with the reporting entity by means of direct or indirect ownership.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.12)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant