Financial Commitments & Contingencies and Key License Agreements - Additional Information (Details) $ in Thousands	1 Months Ended			3 Months Ended		6 Months Ended
	Apr. 30, 2019 USD ($)	Apr. 30, 2018 USD ($)	Apr. 30, 2016 shares	Jun. 30, 2020 USD ($)	Jun. 30, 2019 USD ($)	Jun. 30, 2020 USD ($) product	Jun. 30, 2019 USD ($)	Dec. 31, 2019 USD ($)	Jan. 01, 2019 USD ($)
Long-term Purchase Commitment [Line Items]
Lease cost				$ 594	$ 582	$ 1,189	$ 1,105
Operating lease right-of-use assets - non-current*				3,068		3,068		$ 3,806
Right-of-use asset obtained in exchange for operating lease liability						5,300	$ 4,200
Operating lease liability				3,294		$ 3,294		4,055
Licensors | product						2
Deferrals and contributions				$ 7,600		$ 7,600		$ 8,700
ImmunGene
Long-term Purchase Commitment [Line Items]
Potential payments based on achievement of regulatory milestones						26,100
Asset purchase agreement, upfront payment	$ 2,800
Potential payments based on additional achievements of regulatory milestones						5,000
MD Anderson
Long-term Purchase Commitment [Line Items]
Potential payments based on achievement of regulatory milestones						6,000
Potential payments based on achievement of sales milestones						24,000
Payment Of Upfront Fee		$ 500
SPI-2012
Long-term Purchase Commitment [Line Items]
Issuance (shares) | shares			318,750
Potential payments based on achievement of regulatory milestones						10,000
Potential payments based on achievement of sales milestones						120,000
Poziotinib | Licensing Agreements
Long-term Purchase Commitment [Line Items]
Potential payments based on achievement of regulatory milestones						33,000
Potential payments based on achievement of sales milestones						$ 325,000
ASU 2016-02
Long-term Purchase Commitment [Line Items]
Operating lease right-of-use assets - non-current*									$ 4,200
Operating lease liability									$ 4,200
Minimum
Long-term Purchase Commitment [Line Items]
Remaining lease term				1 year		1 year
Maximum
Long-term Purchase Commitment [Line Items]
Remaining lease term				4 years		4 years