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Line of Credit - Additional Information (Detail)
12 Months Ended
Dec. 31, 2017
USD ($)
Dec. 31, 2016
USD ($)
Debt Instrument [Line Items]    
Total availability under line of credit agreement $ 10,000,000.0  
Borrowings under the line of credit agreement 0 $ 0
Letters of credit outstanding amount 2,700,000  
Available borrowing under letter of credit $ 7,300,000  
Maximum ratio of total liabilities to tangible net worth 2  
Period used for calculating ratios 12 months  
Company's tangible net worth ratio 0.34  
LIBOR    
Debt Instrument [Line Items]    
Debt instrument basis spread on variable rate 1.25%  
Prime Rate    
Debt Instrument [Line Items]    
Debt instrument basis spread on variable rate 0.50%