Segment Reporting - Summary of Segment Revenues, Gross Profit, Segment Operating Income or Loss and Reconciliation of Segment Operating Income or Loss to GAAP Loss (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Segment revenues:
Total Revenue	$ 5,567	$ 7,329	$ 12,118	$ 14,102
Segment gross profit:
Segment gross profit	4,357	5,726	8,867	11,008
Segment operating income (loss):
Segment operating income (loss)	(231)	409	(1,583)	932
General, administrative, depreciation and amortization expense	(2,080)	(1,867)	(4,621)	(3,424)
Interest expense	(115)	(202)	(245)	(411)
Other income	33	64	75	123
Fair value of convertible debentures		(1,915)	(7,464)	(4,440)
Loss on extinguishment of debt			(341)
Loss before income tax expense	(2,393)	(3,511)	(14,179)	(7,220)
Product [Member]
Segment revenues:
Total Revenue	2,888	4,353	6,683	8,175
Service [Member]
Segment revenues:
Total Revenue	2,679	2,976	5,435	5,927
Detection [Member]
Segment gross profit:
Segment gross profit	3,533	4,356	7,000	7,823
Segment operating income (loss):
Segment operating income (loss)	201	673	(145)	975
Detection [Member] | Product [Member]
Segment revenues:
Total Revenue	4,117	5,209	8,593	9,377
Therapy [Member]
Segment gross profit:
Segment gross profit	824	1,370	1,867	3,185
Segment operating income (loss):
Segment operating income (loss)	(432)	(264)	(1,438)	(43)
Therapy [Member] | Service [Member]
Segment revenues:
Total Revenue	$ 1,450	$ 2,120	$ 3,525	$ 4,725