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Income Taxes - Additional Information (Detail) - USD ($)
12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Income Taxes And Tax Related [Line Items]    
Alternative minimum tax credits $ 5,319,000 $ 5,722,000
Allowed tax credit operating losses carry forward 575,000 $ 620,000
Provision for uncertain tax positions 0  
Texas Franchise Tax [Member]    
Income Taxes And Tax Related [Line Items]    
Tax credit operating carry forward losses allowed after the period $ 0  
Tax credit operating carry forward losses allowed after the period, Description No credit may be carried forward past 2026.  
Texas Franchise Tax [Member] | 2015 and 2016 [Member]    
Income Taxes And Tax Related [Line Items]    
Allowed tax credit operating losses carry forward $ 26,000  
Texas Franchise Tax [Member] | 2017 through 2026 [Member]    
Income Taxes And Tax Related [Line Items]    
Allowed tax credit operating losses carry forward $ 89,000