Organization and Basis of Presentation - Additional Information (Detail) $ in Thousands				3 Months Ended
	Sep. 20, 2016 USD ($) shares	Jun. 10, 2016 USD ($) option Indication	Sep. 20, 2014 USD ($)	Sep. 15, 2016 USD ($)	Sep. 30, 2016 USD ($)	Dec. 31, 2015 USD ($)	Sep. 30, 2015 USD ($)	Dec. 31, 2014 USD ($)
Organization And Basis Of Presentation [Line Items]
Cash and cash equivalents					$ 30,716	$ 36,079	$ 46,362	$ 54,059
Net working capital					25,500
Accumulated deficit					$ (119,780)	$ (125,202)
Viventia Bio Inc.
Organization And Basis Of Presentation [Line Items]
Period during which quarterly earn-outs are payable after date of net sales	15 years		15 years
Period in which acquiree is to use commercially reasonable efforts to achieve marketing authorizations	7 years
Roche
Organization And Basis Of Presentation [Line Items]
Up-front license fee under license agreement		$ 7,500
Additional Up-front fee (up to)		$ 262,500
Number of unrelated indications (up to) | Indication		2
Number of option periods provided under license agreement | option		2
Buyout option following first closing of phase II		$ 135,000
Buyout option following first closing of phase II, period		30 days
Buyout option following day after initiation of phase III study		$ 265,000
Buyout option upon non-issuance of patent rights or licensed product		$ 220,000
Period for termination where sufficient development activities are not performed		12 months
First Indication | Roche
Organization And Basis Of Presentation [Line Items]
Amount payable upon achievement of specified milestone (up to)		$ 197,500
Development Milestone | Roche
Organization And Basis Of Presentation [Line Items]
Amount payable upon achievement of specified milestone (up to)		72,500
Regulatory Milestone | Roche
Organization And Basis Of Presentation [Line Items]
Amount payable upon achievement of specified milestone (up to)		50,000
Commercialization Milestone | Roche
Organization And Basis Of Presentation [Line Items]
Amount payable upon achievement of specified milestone (up to)		75,000
Second Indication | Roche
Organization And Basis Of Presentation [Line Items]
Amount payable upon achievement of specified milestone (up to)		$ 65,000
Vicinium | Specified Milestone | Viventia Bio Inc.
Organization And Basis Of Presentation [Line Items]
Percentage of net sales of quarterly earn-out payments during earn-out periods	2.00%		2.00%
EBI-031 | Minimum | Roche
Organization And Basis Of Presentation [Line Items]
Royalty percentage for future products containing EBI-031		7.50%
EBI-031 | Maximum | Roche
Organization And Basis Of Presentation [Line Items]
Royalty percentage for future products containing EBI-031		15.00%
EBI-031 | Development Milestone | Roche
Organization And Basis Of Presentation [Line Items]
Amount payable upon achievement of specified milestone (up to)				$ 22,500
IL-6 | Roche
Organization And Basis Of Presentation [Line Items]
Royalty percentage for future products containing EBI-031		50.00%
Viventia Bio Inc.
Organization And Basis Of Presentation [Line Items]
Common stock issued to selling shareholders (in shares) | shares	4,013,431
Percentage of voting interests acquired	19.90%
Equity interest issued and issuable, equity shares deposited into an escrow account per acquiree (in shares) | shares	401,343
Percentage of common stock owned by acquiree at closing of the share purchase agreement	10.00%
UNITED STATES | Vicinium | Specified Milestone | Viventia Bio Inc.
Organization And Basis Of Presentation [Line Items]
One-time milestone payment upon first sale of product	$ 12,500		$ 12,500
Europe | Vicinium | Specified Milestone | Viventia Bio Inc.
Organization And Basis Of Presentation [Line Items]
One-time milestone payment upon first sale of product	7,000		7,000
JAPAN | Vicinium | Specified Milestone | Viventia Bio Inc.
Organization And Basis Of Presentation [Line Items]
One-time milestone payment upon first sale of product	$ 3,000		$ 3,000