Quarterly report pursuant to Section 13 or 15(d)

Basis of Presentation - Schedule of Amounts Recorded in Prepaid Expenses and Other Assets (Details)

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Basis of Presentation - Schedule of Amounts Recorded in Prepaid Expenses and Other Assets (Details) - USD ($)
$ in Thousands
Jun. 30, 2017
Dec. 31, 2016
Prepaid Expense And Other Assets Current [Abstract]    
Derivative assets [1] $ 6,365  
Prepaid/accrued insurance 3,802 $ 2,924
Surety bond unamortized premiums 2,855 2,462
Prepaid deposits related to royalties 6,155 6,237
Other 2,767 2,881
Prepaid expenses and other assets $ 21,944 $ 14,504
[1] Includes open and closed (and not settled) derivative commodity contracts recorded at fair value.