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Summary of Stock Option Activity Under Black-Scholes Option (Detail) - $ / shares
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Expected term 9 months  
Minimum [Member]    
Expected term   11 months 5 days
Expected volatility 38.10% 38.10%
Risk-free interest rate 1.64% 1.64%
Market value of common stock $ 0.52 $ 0.52
Annual dividend yield 2.23% 2.23%
Forfeiture rate 0.00% 0.00%
Maximum [Member]    
Expected term   1 year 9 months
Expected volatility 41.60% 41.60%
Risk-free interest rate 1.86% 1.86%
Market value of common stock $ 0.76 $ 0.76
Annual dividend yield 3.53% 3.53%
Forfeiture rate 6.80% 6.80%