Patents and Other Intangible Assets - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Finite And Indefinite Lived Intangible Assets [Line Items]
Amortization of intangible assets	$ 1.8	$ 1.8	$ 1.7
Developed Technology [Member]
Finite And Indefinite Lived Intangible Assets [Line Items]
Weighted average amortization period ( in years)	11 years