Financial Commitments & Contingencies and Key License Agreements - Additional Information (Details) - USD ($) $ in Thousands	1 Months Ended		3 Months Ended
	Apr. 30, 2018	Apr. 30, 2016	Mar. 31, 2019	Mar. 31, 2018	Jan. 01, 2019	Dec. 31, 2018
Long-term Purchase Commitment [Line Items]
Operating lease right-of-use assets			$ 3,774
Lease cost			583
Lease cost				$ 400
Present value of operating lease payments			3,922
Lessee, operating lease, lease not yet commenced, amount			700
Potential payments based on achievement of sales milestones			325,000
Deferrals and contributions			7,200			$ 6,200
SPI-2012 [Member]
Long-term Purchase Commitment [Line Items]
Issuance (shares)		318,750
Spi Two Thousand Twelve [Member]
Long-term Purchase Commitment [Line Items]
Potential payments based on achievement of regulatory milestones			13,000
Potential payments based on achievement of sales milestones			225,000
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	$ 11,000
Potential payments based on achievement of sales milestones	$ 23,000
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