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Claim Settlement Receivable (Details) - USD ($)
$ in Thousands
3 Months Ended
Oct. 03, 2016
Mar. 24, 2016
Mar. 31, 2017
Mar. 31, 2016
Dec. 31, 2016
Receivables with Imputed Interest [Line Items]          
Litigation settlement receivable     $ 7,863   $ 7,804
Litigation settlement gain (loss)     0 $ 12,548  
BP Exploration & Production Inc.          
Receivables with Imputed Interest [Line Items]          
Litigation settlement receivable, gross   $ 13,200      
Litigation settlement receivable   12,500 8,200    
Litigation settlement amount received $ 5,000        
Litigation settlement receivable due in October 2017, 2018 and 2019   $ 2,700      
Imputed interest rate on litigation settlement receivable   3.00%      
Unamortized discount   $ 700      
Interest income     $ 100    
Other income | BP Exploration & Production Inc.          
Receivables with Imputed Interest [Line Items]          
Litigation settlement gain (loss)       $ 12,500