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Fair Value Measurements - Additional Information (Detail) |  | 12 Months Ended |
--- | --- | --- | ---
Jun. 10, 2014 shares | Dec. 31, 2016 USD ($) CommercialTest shares | Dec. 31, 2015 USD ($) shares | Jun. 15, 2016 shares
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |  |  |
Transfers between Level 1, Level 2 and Level 3 categories during the periods | $ |  | $ 0 | $ 0 |
Warrants outstanding |  |  |  | 1,002,507
Fair Value Measured Using - (Level 3) [Member] |  |  |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |  |  |
Warrants outstanding |  | 2,978,087 |  |
ImmuMetrix, Inc. [Member] |  |  |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |  |  |
Contingent obligation to issue common stock | 911,364 |  |  |
Milestone description |  | the milestone will be achieved if the Company completes 2,500 commercial tests involving the measurement of dd-cfDNA in organ transplant recipients in the United States no later than six years after the closing date of the acquisition. |  |
ImmuMetrix, Inc. [Member] | Contingent consideration [Member] |  |  |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |  |  |
Contingent obligation to issue common stock |  | 227,845 | 227,845 |
Number of commercial tests involving the measurement of cfDNA to be completed | CommercialTest |  | 2,500 |  |
Milestone description |  | The issuance will occur if the Company completes 2,500 commercial tests involving the measurement of dd-cfDNA in organ transplant recipients in the United States by June 10, 2020. |  |
Probability of the achievement |  | 80.00% | 65.00% |

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