Financial Commitments & Contingencies and Key License Agreements - Additional Information (Details) $ in Thousands		1 Months Ended			3 Months Ended		6 Months Ended
	Mar. 01, 2019 product	Apr. 30, 2019 USD ($) product	Apr. 30, 2018 USD ($)	Apr. 30, 2016 shares	Jun. 30, 2019 USD ($)	Jun. 30, 2018 USD ($)	Jun. 30, 2019 USD ($)	Jun. 30, 2018 USD ($)	Jan. 01, 2019 USD ($)	Dec. 31, 2018 USD ($)
Long-term Purchase Commitment [Line Items]
Operating lease right-of-use assets					$ 3,842		$ 3,842			$ 0
Present value of operating lease payments					4,071		4,071
Lease cost					582	$ 400	1,105	$ 900
Potential payments based on achievement of sales milestones							325,000
Number of products | product	7
Deferrals and contributions					$ 7,400		7,400			$ 6,200
SPI-2012 [Member]
Long-term Purchase Commitment [Line Items]
Issuance (shares) | shares				318,750
Spi Two Thousand Twelve [Member]
Long-term Purchase Commitment [Line Items]
Potential payments based on achievement of regulatory milestones							10,000
Potential payments based on achievement of sales milestones							120,000
Poziotinib [Member] | Licensing Agreements [Member]
Long-term Purchase Commitment [Line Items]
Potential payments based on achievement of regulatory milestones							$ 33,000
MD Anderson [Member]
Long-term Purchase Commitment [Line Items]
Potential payments based on achievement of regulatory milestones			$ 9,000
Potential payments based on achievement of sales milestones			$ 30,000
Accounting Standards Update 2016-02 [Member]
Long-term Purchase Commitment [Line Items]
Operating lease right-of-use assets									$ 4,200
Present value of operating lease payments									$ 4,200
Minimum [Member]
Long-term Purchase Commitment [Line Items]
Lessee, operating lease, remaining lease term							1 year
Maximum [Member]
Long-term Purchase Commitment [Line Items]
Lessee, operating lease, remaining lease term							5 years
ImmunGene, Inc. [Member]
Long-term Purchase Commitment [Line Items]
Potential payments based on achievement of regulatory milestones							$ 26,100
Potential payments based on additional achievements of regulatory milestones							$ 5,000
Number of products | product		2
Asset purchase agreement, upfront payment		$ 2,800