Segment Information - Additional Information (Detail) $ in Thousands	3 Months Ended								12 Months Ended
	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 ($) Segment	Dec. 31, 2017 USD ($)
Revenue, Major Customer [Line Items]
Number of reporting segment | Segment									1
Revenue realized for one-time upfront license fee	$ 5,227	$ 4,914	$ 5,438	$ 5,613	$ 4,858	$ 8,677	$ 5,587	$ 6,091	$ 21,192	$ 25,213
Upfront License Fee [Member]
Revenue, Major Customer [Line Items]
Revenue realized for one-time upfront license fee	$ 596	$ 595	$ 658	$ 528	$ 509	4,385	$ 914	$ 950	$ 2,377	$ 6,758
Upfront License Fee [Member] | Verance Corporation [Member]
Revenue, Major Customer [Line Items]
Revenue realized for one-time upfront license fee						$ 3,500
Customer Concentration Risk [Member] | Minimum [Member] | Sales [Member]
Revenue, Major Customer [Line Items]
Percentage of revenue from major customers									10.00%	10.00%