Related Party Transaction - Additional Information (Detail) - USD ($)		12 Months Ended
	Apr. 04, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Related Party Transaction [Line Items]
Contract revenue		$ 13,401,000	$ 12,804,000	$ 18,860,000
Research Collaboration Agreement [Member] | AnGes MG, Inc [Member]
Related Party Transaction [Line Items]
Percentage of common stock outstanding	18.60%
Non- refundable amount receivable under research collaboration agreement	$ 750,000
Contract revenue		$ 500,000