Subsequent Event - Additional Information (Detail) $ in Millions	1 Months Ended
Aug. 31, 2018 USD ($)
Taiho Pharmaceutical Co Ltd \| Option and License Agreement \| Subsequent Event
Subsequent Event [Line Items]
Payment for option exercise	$ 3.0

Detail information of subsequent event by type. User is expected to use existing line items from elsewhere in the taxonomy as the primary line items for this disclosure, which is further associated with dimension and member elements pertaining to a subsequent event.

No definition available.

Name:	us-gaap_SubsequentEventLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration