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Income Taxes - Components of Net Deferred Tax Assets and Liabilities (Detail) - USD ($)
$ in Thousands
Dec. 31, 2020
Dec. 31, 2019
Deferred Tax Assets:    
Accrued liabilities $ (584) $ 614
Allowance for doubtful accounts 136 95
Derivative Contracts 153 110
Alternative minimum tax credits 0 1,720
State Net operating loss carry-forwards 760 821
Total deferred tax assets 465 3,360
Deferred Tax Liabilities:    
Basis differences relating to managed partnerships 544 2,109
Depletion and depreciation 36,288 37,173
Total deferred tax liabilities 39,832 39,282
Net deferred tax liabilities $ 36,367 $ 35,922