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Employee Retirement Plans - Global Marine Personal Pension Plan Narrative (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]    
Defined benefit, maximum employees contributions percentage 6.00%  
Defined benefit, matching contribution amount $ 0.1 $ 0.1
Global Marine Personal Pension Plan | Global Marine Personal Pension Plan    
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]    
Defined benefit, minimum employees contributions percentage 2.00%  
Defined benefit, maximum employees contributions percentage 7.50%  
Defined benefit, employer matching rate plus an additional fixed contributions percentage (as a percent) 5.00%  
Defined benefit, matching contribution amount $ 1.4 $ 1.7
Global Marine Personal Pension Plan | Global Marine Personal Pension Plan | Ex Care    
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]    
Defined benefit, minimum employees contributions percentage 2.50%  
Defined benefit, maximum employees contributions percentage 7.50%