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Summary of Operations and Significant Accounting Policies - Summary of Allowance for Doubtful Accounts (Detail) - USD ($)
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Receivables [Abstract]      
Allowance for doubtful accounts, beginning balance $ 265,000 $ 78,000 $ 268,000
Charges to expense 268,000 192,000 (115,000)
Write-offs of uncollectible accounts, net of recoveries   (5,000) (75,000)
Allowance for doubtful accounts, ending balance $ 533,000 $ 265,000 $ 78,000