Segment Reporting - Summary of Segment Revenues, Segment Operating Income or Loss and Reconciliation of Segment Operating Income or Loss to GAAP Loss (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Segment revenues:
Total revenue	$ 8,520	$ 7,930
Segment operating income (loss):
Segment operating income (loss)	(460)	(328)
General and administrative expenses	(1,748)	(1,672)
Interest expense	(817)	(826)
Gain on fair value of warrant	1,136	431
Other income	4	6
Loss before income tax expense	(137)	(717)
Detection [Member]
Segment revenues:
Total revenue	4,175	4,638
Segment operating income (loss):
Segment operating income (loss)	1,516	1,574
Therapy [Member]
Segment revenues:
Total revenue	4,345	3,292
Segment operating income (loss):
Segment operating income (loss)	(228)	(230)
All Reporting Segments [Member]
Segment operating income (loss):
Segment operating income (loss)	$ 1,288	$ 1,344