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Credit Agreement - Additional Information (Detail) - Credit Agreement [Member] - Unsecured Line of Credit Agreement [Member] - USD ($)
1 Months Ended
Sep. 30, 2016
Sep. 30, 2015
Sep. 30, 2018
Line Of Credit Facility [Line Items]      
Line of credit, final due month and year 2018-09    
Line of credit, amount outstanding     $ 0
JPMorgan Chase Bank, N.A. [Member]      
Line Of Credit Facility [Line Items]      
Line of credit, term   2 years  
Line of credit, maximum borrowing capacity   $ 12,000,000