Related Party Transactions - Additional Information (Detail)		3 Months Ended		9 Months Ended		12 Months Ended
	Feb. 01, 2017	Sep. 30, 2018 USD ($) ft²	Mar. 31, 2015	Sep. 30, 2018 USD ($) ft²	Sep. 30, 2017 USD ($)	Dec. 31, 2017 USD ($)
San Diego California Facility [Member]
Related Party Transaction [Line Items]
Lease expiration date	Mar. 31, 2017
Rental income		$ 0		$ 0	$ 51,000	$ 51,000
Aegea Biotechnologies, Inc [Member]
Related Party Transaction [Line Items]
Reimbursement for shared patent costs		$ 0		$ 19,000		$ 15,000
Nonexecutive [Member] | San Diego California Facility [Member]
Related Party Transaction [Line Items]
Leased facility, expansion of original premises | ft²		9,849		9,849
Lease agreement date of commencement				Mar. 30, 2015
Leased facility, rent expense per month				$ 12,804
Lease facility, refundable security deposit amount		$ 12,804		12,804
Lease expiration date			Jul. 31, 2015
Lease agreement, amount of security deposit applied against additional rents owed				16,000
Lease agreement, amount of additional rents waived				$ 3,200