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Income Taxes - Components of Net Deferred Tax Assets and Liabilities (Detail) - USD ($)
$ in Thousands
Dec. 31, 2016
Dec. 31, 2015
Deferred Tax Assets:    
Accrued liabilities $ 550 $ 593
Allowance for doubtful accounts 152 188
Derivative Contracts 1,273 3
Alternative minimum tax credits 6,612 5,319
Net operating loss carry-forwards 586 575
Percentage depletion carry-forwards 3,025 3,751
Total deferred tax assets 12,198 10,429
Deferred Tax Liabilities:    
Basis differences relating to managed partnerships 6,211 6,238
Depletion and depreciation 43,487 41,290
Derivative contracts   250
Total deferred tax liabilities 49,698 47,778
Net non-current deferred income tax liabilities $ 37,500 $ 37,349