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Contract Balances - Additional Information (Detail) - USD ($)
3 Months Ended 12 Months Ended
Mar. 31, 2018
Dec. 31, 2017
Jan. 01, 2018
Accounts Notes And Loans Receivable [Line Items]      
Current unbilled receivables $ 4,800,000   $ 700,000
Non-Current unbilled receivables 500,000   600,000
Customer One [Member]      
Accounts Notes And Loans Receivable [Line Items]      
Customer account balance $ 9,099,000 $ 10,159,000  
Customer One [Member] | Customer Concentration Risk [Member] | Accounts Receivable [Member]      
Accounts Notes And Loans Receivable [Line Items]      
Percentage of Accounts receivable 22.00% 34.00%  
Customer Two [Member]      
Accounts Notes And Loans Receivable [Line Items]      
Customer account balance $ 4,687,000 $ 8,990,000  
Customer Two [Member] | Customer Concentration Risk [Member] | Accounts Receivable [Member]      
Accounts Notes And Loans Receivable [Line Items]      
Percentage of Accounts receivable 11.00% 30.00%  
Minimum [Member] | Customer Concentration Risk [Member] | Accounts Receivable [Member]      
Accounts Notes And Loans Receivable [Line Items]      
Percentage of Accounts receivable 10.00% 10.00%  
Balances Prior to Adoption of ASC 606 [Member] | ASU 2014-09 [Member]      
Accounts Notes And Loans Receivable [Line Items]      
Unbilled receivables for contract assets     $ 0
Roche [Member] | Sample Profiling Services [Member]      
Accounts Notes And Loans Receivable [Line Items]      
Revenue recognized $ 3,900