Quarterly report pursuant to Section 13 or 15(d)

Basis of Presentation and Accounting Policies Property and Equipment (Details)

v3.7.0.1
Basis of Presentation and Accounting Policies Property and Equipment (Details)
$ in Millions
6 Months Ended
Jun. 30, 2017
USD ($)
Property, Plant and Equipment [Line Items]  
Capitalized Interest Costs, Including Allowance for Funds Used During Construction $ 2.3
Wind Farm Utility Vessel [Member]  
Property, Plant and Equipment [Line Items]  
Property, Plant and Equipment, Useful Life 10 years
Offshore Support Vessels [Member]  
Property, Plant and Equipment [Line Items]  
Property, Plant and Equipment, Useful Life 20 years