Annual report pursuant to Section 13 and 15(d)

Significant Accounting Policies - Schedule of Amounts Recorded in Prepaid Expenses and Other Assets (Details)

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Significant Accounting Policies - Schedule of Amounts Recorded in Prepaid Expenses and Other Assets (Details) - USD ($)
$ in Thousands
Dec. 31, 2018
Dec. 31, 2017
Prepaid Expense And Other Assets Current [Abstract]    
Derivatives - current $ 60,687  
Prepaid/accrued insurance 2,987 $ 2,401
Surety bonds unamortized premiums 2,210 2,676
Prepaid deposits related to royalties 8,872 6,456
Advances for capital expenditures 745  
Other 905 1,886
Prepaid expenses and other assets $ 76,406 $ 13,419