Annual report pursuant to Section 13 and 15(d)

Business Segments and Customer Information (Narrative) (Details)

v3.8.0.1
Business Segments and Customer Information (Narrative) (Details)
$ in Millions
12 Months Ended
Dec. 31, 2017
segment
Dec. 31, 2016
USD ($)
Segment Reporting Information [Line Items]    
Number of reportable operating segments | segment 3  
Corporate    
Segment Reporting Information [Line Items]    
Gain resulting from the combined effect of the Anchorage Lawsuit and Maritime Administration settlements   $ 1.4
Corporate | Heritage Litigation    
Segment Reporting Information [Line Items]    
Settlement amount   $ 3.3