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Credit Facility - Additional Information (Detail) - USD ($)
3 Months Ended
Mar. 31, 2019
Mar. 31, 2018
Dec. 31, 2018
Line of Credit Facility [Line Items]      
Debt fee $ 1,558,000   $ 728,000
Accretion of debt discount 145,000 $ 56,000  
Amortization of deferred financing cost 63,000 $ 60,000  
Senior Secured Revolving Credit Facility      
Line of Credit Facility [Line Items]      
Revolving credit facility 47,500,000   $ 44,500,000
Undrawn availability $ 12,500,000