Annual report pursuant to Section 13 and 15(d)

Significant Accounting Policies - Schedule of Other Liabilities (Long-term) (Details)

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Significant Accounting Policies - Schedule of Other Liabilities (Long-term) (Details) - USD ($)
$ in Thousands
Dec. 31, 2018
Dec. 31, 2017
Other Liabilities Disclosure [Abstract]    
Apache lawsuit $ 49,500 $ 49,500
Uncertain tax positions including interest/penalties 11,523 11,015
Dispute related to royalty deductions 4,787  
Dispute related to royalty-in-kind 2,135 914
Other 745 5,437
Total other liabilities (long-term) $ 68,690 $ 66,866