Amount of revenue recognized that was previously included in balance of obligation to transfer good or service to customer for which consideration from customer has been received or is due.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 8
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109196051&loc=SL49130549-203045

Name:	us-gaap_ContractWithCustomerLiabilityRevenueRecognized
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Collaboration Agreements - Product Revenue - Additional Information 5 (Detail) - Astellas Agreement [Member] - Japan [Member] - USD ($) $ in Millions	1 Months Ended	3 Months Ended	12 Months Ended
	Dec. 31, 2018	Jun. 30, 2018	Dec. 31, 2018
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Contract with customer liability, revenue recognized	$ 43.9	$ 20.9
Product Revenue [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Contract with customer liability, revenue recognized			$ 64.8