Licensing and Other Revenue - Additional Information (Detail)	1 Months Ended			3 Months Ended								12 Months Ended
	Jul. 31, 2013 USD ($)	Jun. 30, 2013 USD ($)	Jun. 30, 2013 EUR (€)	Dec. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Jun. 30, 2013 EUR (€)
Licensing And Other Revenue [Line Items]
Description of agreement expire term												The agreement will expire at the later of the last-to-expire patent in the EEA or ten years from the first commercial sale of the test in the EEA, which occurred in 2014.
Common stock value				$ 41,000				$ 29,000				$ 41,000	$ 29,000
Upfront cash payment		$ 408,000	€ 387,500
Refundable upfront payments		263,000	€ 250,000
Revenues recognized from the arrangement												39,000	39,000	$ 2,000
Royalty revenues				23,509,000	$ 21,184,000	$ 17,823,000	$ 14,053,000	12,503,000	$ 12,191,000	$ 12,046,000	$ 11,584,000	76,569,000	48,324,000	40,631,000
Royalty revenues receivable balance				$ 0				$ 0				0	0
Royalty [Member]
Licensing And Other Revenue [Line Items]
Royalty revenues												$ 300,000	$ 500,000	$ 200,000
Diaxonhit [Member]
Licensing And Other Revenue [Line Items]
Common stock value		$ 408,000													€ 387,500
Shares sold for consideration	$ 467,000