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Company Overview (Details) $ in Thousands | 1 Months Ended | 6 Months Ended | 12 Months Ended
--- | --- | --- | ---
Feb. 29, 2016 USD ($) | Jan. 31, 2016 USD ($) renewal_option | Feb. 28, 2014 vessel | Jun. 30, 2016 USD ($) segment vessel | Jun. 30, 2015 USD ($) | Dec. 31, 2017
Segment Reporting Information [Line Items] |  |  |  |  |  |
Number of reportable segments | segment |  |  |  | 3 |  |
Sale of ownership interest for cash |  |  |  | $ 25,000 | $ 0 |
Scotland |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |
Proceeds from sale of property |  | $ 11,000 |  |  |  |
Term of agreement |  | 15 years |  |  |  |
Number of renewal options | renewal_option |  | 2 |  |  |  |
Term of renewal option |  | 5 years |  |  |  |
Gain from sale of property |  | $ 7,600 |  |  |  |
Deepwater Gateway, L.L.C. [Member] |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |
Sale of ownership interest for cash | $ 25,000 |  |  |  |  |
Robotics [Member] |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |
Number of chartered vessels | vessel |  |  |  | 3 |  |
Q5000 [Member] | Forecast [Member] |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |
Minimum contracted vessel days |  |  |  |  |  | 270 days
Monohull Vessels [Member] |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |
Number of chartered vessels | vessel |  |  | 2 |  |  |
Monohull Vessels [Member] | Well Intervention [Member] |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |
Number of chartered vessels | vessel |  |  |  | 2 |  |

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- Definition Amount of gain (loss) on sale or disposal of property, plant and equipment assets, including oil and gas property and timber property. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=66902209&loc=d3e3602-108585 + Details
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