The Company, Business Activities and Basis of Presentation - Additional Information (Detail)		3 Months Ended	9 Months Ended
	Jul. 06, 2018 shares	Sep. 30, 2017 USD ($) $ / shares	Sep. 30, 2018 shares	Sep. 30, 2017 USD ($) $ / shares	Dec. 31, 2017 shares
The Company Business Activities And Basis Of Presentation [Line Items]
Stockholders equity reverse stock split ratio	0.03
Common stock, shares authorized | shares	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.
Nonrecurring net revenue recognized on accrual basis associated with cases delivered | $		$ 102,000		$ 839,000
Increase (decrease) in net income (loss) per common share on nonrecurring net revenue | $ / shares		$ (0.10)		$ (0.97)
Net revenue recorded in excess of commercial cash collections | $		$ 125,000		$ 1,158,000
Increase decrease in net income (loss) per common share | $ / shares		$ (0.13)		$ (1.35)
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