DESCRIPTION OF BUSINESS (Details) $ in Thousands	1 Months Ended	6 Months Ended		12 Months Ended
	Sep. 30, 2016 USD ($) shares	Jun. 30, 2021 USD ($) segment	Jun. 30, 2020 USD ($)	Dec. 31, 2020 USD ($)
Variable Interest Entity [Line Items]
Number of operating segments | segment		1
Cash and cash equivalents		$ 151,036		$ 52,389
Net working capital		156,300
Accumulated deficit		396,875		315,921
Negative cash flows from operating activities incurred		$ (41,616)	$ (18,326)	$ (30,800)
Viventia Bio, Inc.
Variable Interest Entity [Line Items]
Shares of common stock issued to the selling shareholders (in shares) | shares	4,000,000.0
Percentage of voting interests acquired (as a percent)	19.90%
One-time milestone payment upon first sale of product	$ 12,500
Period during which quarterly earn-outs are payable after date of net sales	15 years
Period in which acquiree is to use commercially reasonable efforts to achieve marketing authorizations	7 years
Viventia Bio, Inc. | Vicinium | Collaborative Arrangement, Revenue based on Specified Milestone
Variable Interest Entity [Line Items]
Percentage of net sales of quarterly earn-out payments during earn-out periods	2.00%
Viventia Bio, Inc. | Vicinium | Europe | Collaborative Arrangement, Revenue based on Specified Milestone
Variable Interest Entity [Line Items]
One-time milestone payment upon first sale of product	$ 7,000
Viventia Bio, Inc. | Vicinium | Japan | Collaborative Arrangement, Revenue based on Specified Milestone
Variable Interest Entity [Line Items]
One-time milestone payment upon first sale of product	$ 3,000