Contingent Liability Related to the Anawah Acquisition - Additional Information (Detail) $ in Thousands		6 Months Ended
	Dec. 31, 2010 USD ($) Program	Jun. 30, 2018 USD ($)	Dec. 31, 2017 USD ($)	Jun. 15, 2005 USD ($)
Commitments And Contingencies [Line Items]
Other noncurrent liability		$ 3,000	$ 3,000
Anawah, Inc [Member]
Commitments And Contingencies [Line Items]
Contingent liability	$ 3,000			$ 5,000
Date of merger and reorganization		Jun. 15, 2005
Restructuring activities, description		As of December 31, 2010, the Company ceased activities relating to three of the six Anawah product programs,
Number of development programs ceased | Program	3
Number of development programs | Program	6
Other noncurrent liability		$ 3,000