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Commitments - Additional Information (Detail) - USD ($)
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Feb. 28, 2019
Rent expense for office space $ 659,000 $ 659,000  
Subsequent Event [Member]      
Lease Payments With in One Year     $ 344,000
Lease Payments Due Next year     $ 86,000