Amount, before allowance for credit loss, of right to consideration in exchange for good or service transferred to customer, when right is conditioned on something other than passage of time.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=82913815&loc=SL49130531-203044

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 8
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=109196051&loc=SL49130549-203045

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 45
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=82913815&loc=SL49130533-203044

Name:	us-gaap_ContractWithCustomerAssetGross
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Revenue from Contracts with Customers - Additional Information (Detail) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2018 USD ($)	Sep. 30, 2018 USD ($) Product	Jan. 01, 2018 USD ($)
ADCETRIS [Member]
Revenue from Contracts with Customers [Line Items]
Number of marketed product \| Product		1
Collaboration and License Agreement Revenues [Member]
Revenue from Contracts with Customers [Line Items]
Deferred revenue recognized		$ 26.0
Collaboration and License Agreement Revenues [Member] \| Takeda Collaboration and License Agreement [Member]
Revenue from Contracts with Customers [Line Items]
Milestone payment revenue	$ 10.0	10.0
Accounting Standards Update 2014-09 [Member] \| ADCETRIS [Member]
Revenue from Contracts with Customers [Line Items]
Contract asset	$ 1.0	$ 1.0	$ 12.7