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Income Taxes - Additional Information (Detail) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Income Tax Expense Benefit [Line Items]    
Reclass of AMT credit carryforward to current federal expense   $ 400
Unutilized alternative minimum tax credit carryforwards partially refundable year one 2019  
Unutilized alternative minimum tax credit carryforwards partially refundable year two 2020  
Unutilized alternative minimum tax credit carryforwards partially refundable year three 2021  
Unutilized alternative minimum tax credit carryforwards fully refundable year 2022  
Tax expense related to The Job Cuts and Tax Act (“Tax Act”), primarily due to reduction in corporate tax rate   6,796
Corporate federal income tax rate 21.00%  
Valuation allowance against our deferred tax assets $ 797 $ 602
Domestic Tax Authority [Member]    
Income Tax Expense Benefit [Line Items]    
Net operating loss carryforward $ 37,500  
Expiration of net operating loss carryforwards Loss carryforwards for federal tax purposes will expire between 2020 and 2038 if not utilized  
Losses expected to expire unused $ 17,600  
Maximum annual limitation of federal net operating losses 1,000  
Domestic Tax Authority [Member] | Research and Development [Member]    
Income Tax Expense Benefit [Line Items]    
Research and development credit carryforwards $ 3,000  
Year in which credit carryforward begins to expire 2030  
State and Local Jurisdiction [Member]    
Income Tax Expense Benefit [Line Items]    
Net operating loss carryforward $ 4,100  
Expiration of net operating loss carryforwards Loss carryforwards for state tax purposes will expire between 2019 and 2031 if not utilized  
State and Local Jurisdiction [Member] | Net Operating Loss and Credit Carryforwards [Member]    
Income Tax Expense Benefit [Line Items]    
Valuation allowance against our deferred tax assets $ 800  
State and Local Jurisdiction [Member] | Research and Development [Member]    
Income Tax Expense Benefit [Line Items]    
Research and development credit carryforwards $ 1,000  
Year in which credit carryforward begins to expire 2025