Presage License Agreement - Additional Information (Detail) - USD ($)	1 Months Ended	3 Months Ended		6 Months Ended
	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 2016
Related Party Transaction [Line Items]
Research and development expenses		$ 3,444,000	$ 1,642,000	$ 9,508,000	$ 3,288,000
Presage License Agreement | Presage Biosciences, Inc.
Related Party Transaction [Line Items]
Payment for license upfront fees	$ 1,900,000
Compensation payable for grant of rights	4,900,000
Presage License Agreement | Presage Biosciences, Inc. | Additional Near Term Payment | Accrued Liabilities
Related Party Transaction [Line Items]
Compensation payable for grant of rights		$ 1,000,000		1,000,000
Presage License Agreement | Presage Biosciences, Inc. | Potential Payments on Achievement of Development Regulatory and Commercial Milestones | Maximum
Related Party Transaction [Line Items]
Milestone payments payable amount	179,000,000
Presage License Agreement | Presage Biosciences, Inc. | Incremental Payment
Related Party Transaction [Line Items]
Compensation payable for grant of rights	$ 2,000,000
Presage License Agreement | Presage Biosciences, Inc. | Up-front and near term payments
Related Party Transaction [Line Items]
Research and development expenses				$ 2,900,000