Adoption of ASC Topic 606, "Revenue from Contracts with Customers" - Additional Information (Detail) - Topic 606 [Member]	3 Months Ended	9 Months Ended
	Sep. 30, 2018 USD ($)	Sep. 30, 2018 USD ($)
Revenue Initial Application Period Cumulative Effect Transition [Line Items]
Impact of adoption of Topic 606 (Note 5)		$ 2,371,000
Impact to revenues	$ (82,000)	$ (246,000)
Revenue From License Agreement [Member] | Minimum [Member]
Revenue Initial Application Period Cumulative Effect Transition [Line Items]
Revenue, remaining performance obligation, expected timing of satisfaction, period	10 years	10 years
Revenue From License Agreement [Member] | Maximum [Member]
Revenue Initial Application Period Cumulative Effect Transition [Line Items]
Revenue, remaining performance obligation, expected timing of satisfaction, period	20 years	20 years