Fair Value Measurements - Additional Information (Detail)	3 Months Ended		6 Months Ended	12 Months Ended
	Jun. 30, 2017 USD ($) shares	Mar. 31, 2017	Jun. 30, 2017 USD ($) CommercialTest shares	Dec. 31, 2016 USD ($) shares	Mar. 15, 2017 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
JGB Debt [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Warrant to purchase stock, shares	1,250,000		1,250,000		1,250,000
Fair Value Measured Using - (Level 3) [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Decrease in fair value of contingent consideration | $			$ 5,480,000
Warrants outstanding	2,978,087		2,978,087
Fair Value Measured Using - (Level 3) [Member] | Contingent Consideration Liability [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Decrease in fair value of contingent consideration | $	$ 100,000		$ 285,000
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
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.
Number of commercial tests involving the measurement of cfDNA to be completed | CommercialTest			2,500
Probability of the achievement		85.00%	85.00%	80.00%