Financial Commitments & Contingencies and Key License Agreements - Additional Information (Details) $ in Thousands	1 Months Ended			3 Months Ended
	Apr. 30, 2019 USD ($)	Apr. 30, 2018 USD ($)	Apr. 30, 2016 shares	Mar. 31, 2020 USD ($) product	Mar. 31, 2019 USD ($)	Dec. 31, 2019 USD ($)	Jan. 01, 2019 USD ($)
Long-term Purchase Commitment [Line Items]
Lease cost				$ 595	$ 583
Operating lease right-of-use assets - non-current				3,467		$ 3,806
Right-of-use asset obtained in exchange for operating lease liability				5,300	$ 4,200
Operating lease liability				$ 3,706		4,055
Licensors | product				2
Deferrals and contributions				$ 7,400		$ 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
Maximum
Long-term Purchase Commitment [Line Items]
Remaining lease term				4 years