The Company, Business Activities and Basis of Presentation - Additional Information (Detail)		3 Months Ended
	Jul. 06, 2018 shares	Mar. 31, 2019 shares	Dec. 31, 2018 shares
The Company Business Activities And Basis Of Presentation [Line Items]
Stockholders equity reverse stock split ratio	0.03
Common stock, shares authorized	150,000,000	150,000,000	150,000,000
Description of reverse stock split	On July 6, 2018, the Company’s stockholders approved, and the Company filed, an amendment to the Company’s Certificate of Amendment of Certificate of Incorporation to effect a one-for-thirty reverse stock split of the Company’s outstanding common stock.
ASC 606 [Member]
The Company Business Activities And Basis Of Presentation [Line Items]
Performance obligation, description of timing		The duration of time between accession receipt and delivery of a valid assay result to the ordering physician or entity is typically less than two weeks.
Practical expedient, description		The Company does not adjust the transaction price for the effects of a significant financing component, as at contract inception, the Company expects the collection cycle to be one year or less.
ASC 606 [Member] | Maximum [Member] | Sales and Marketing Expenses [Member]
The Company Business Activities And Basis Of Presentation [Line Items]
Amortization period		1 year