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Income Taxes - Components of Net Deferred Tax Assets and Liabilities (Detail) - USD ($)
$ in Thousands
Dec. 31, 2018
Dec. 31, 2017
Deferred Tax Assets:    
Accrued liabilities $ 519 $ 349
Allowance for doubtful accounts 51 22
Derivative Contracts 0 684
Disallowed Interest Carryforwards 769 0
Alternative minimum tax credits 4,760 9,919
State Net operating loss carry-forwards 469 528
Percentage depletion carry-forwards 727
General Business Credits 137
Total deferred tax assets 6,705 12,229
Deferred Tax Liabilities:    
Basis differences relating to managed partnerships 2,296 3,193
Depletion and depreciation 36,711 33,998
Derivative Contracts 526
Total deferred tax liabilities 39,533 37,191
Net deferred tax liabilities $ 32,828 $ 24,962