Commitments and Contingencies - Additional Information (Detail)	1 Months Ended						3 Months Ended		9 Months Ended		12 Months Ended
	Apr. 30, 2018	Nov. 30, 2017 USD ($)	Dec. 31, 2015 USD ($)	Nov. 30, 2015 USD ($) shares	Sep. 30, 2015 ft²	Feb. 28, 2015 ft²	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($) Milestone	Sep. 30, 2017 USD ($)	Dec. 31, 2017 Milestone
Other Commitments [Line Items]
Rental expense							$ 42,000	$ 252,000	$ 126,000	$ 455,000
Number of milestones achieved | Milestone									0		0
Indemnification obligations amount							0		$ 0
Contingent liabilities							$ 0		$ 0
License Agreement [Member]
Other Commitments [Line Items]
Sales based milestone payment			$ 36,000,000
Royalty payment period			8 years
License Agreement [Member] | Maximum [Member]
Other Commitments [Line Items]
Development and regulatory milestone payments			$ 42,100,000
License Agreement [Member] | Minimum [Member]
Other Commitments [Line Items]
Sales required to achieve milestone payment			1,000,000,000
Office of Chief Scientist of Israeli Ministry of Economy and Industry [Member]
Other Commitments [Line Items]
Grants received			$ 537,000
Scientific Development and Research, Inc. and Otodyne, Inc. [Member] | License Agreement [Member]
Other Commitments [Line Items]
Share issued as consideration | shares				9,780
Scientific Development and Research, Inc. and Otodyne, Inc. [Member] | License [Member] | License Agreement [Member]
Other Commitments [Line Items]
License fees paid				$ 750,000
Sublease [Member]
Other Commitments [Line Items]
Area of office space | ft²						15,981
Lease commenced date						Apr. 01, 2015
Leases expiration date						Dec. 31, 2016
Leases extension date						Jul. 31, 2018
Additional advance rent paid for lease termination		$ 455,000
Three-year Operating Lease [Member]
Other Commitments [Line Items]
Area of office space | ft²					5,197
Leases expiration date					Aug. 31, 2018
Leases extension date	Sep. 30, 2021
Operating lease expiration term					3 years