Equity Investments - Narrative (Details) $ in Thousands	6 Months Ended
Jun. 30, 2018 USD ($) ft	Dec. 31, 2017 USD ($)
Schedule of Equity Method Investments [Line Items]
Investee losses in excess of investment	$ 6,518	$ 7,567
Independence Hub, LLC
Schedule of Equity Method Investments [Line Items]
Percentage of ownership interest	20.00%
Water depth \| ft	8,000
Investee losses in excess of investment	$ 8,800	$ 9,800

The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 323
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=114001798&loc=d3e33918-111571

Name:	us-gaap_EquityMethodInvestmentOwnershipPercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant