Development Derivative Liability - Narrative (Details)	1 Months Ended	6 Months Ended
	Jan. 31, 2020 USD ($)	Jun. 30, 2020 USD ($) tranche $ / shares shares	Dec. 31, 2019 USD ($) shares
Derivative [Line Items]
Common stock, shares issued (in shares) | shares		28,891,534	28,796,371
Common stock, shares issued, value		$ 29,000	$ 29,000
Derivative
Derivative [Line Items]
Initial payment, net of common stock warrants		2,100,000
Funding during the period		8,400,000
Change in fair value		4,200,000
SFJ Agreement
Derivative [Line Items]
Potential milestones payment		$ 120,000,000.0
Cost of borrowing rate		16.00%
SFJ Pharmaceuticals
Derivative [Line Items]
Cost of borrowing rate		2.50%
Collaborative Arrangement, Transaction with Party to Collaborative Arrangement | SFJ Agreement
Derivative [Line Items]
Common stock, shares issued (in shares) | shares		2,200,000
Shares issued (in usd per share) | $ / shares		$ 6.50
Common stock, shares issued term		10 years
Number of tranches | tranche		2
Common stock, shares issued, value		$ 7,900,000
Collaborative Arrangement, Transaction with Party to Collaborative Arrangement | SFJ Agreement | Derivative
Derivative [Line Items]
Initial payment, net of common stock warrants		2,075,000
Funding during the period		8,449,000
Change in fair value		$ (4,162,000)
Collaborative Arrangement, Transaction with Party to Collaborative Arrangement | SFJ Agreement | Tranche A
Derivative [Line Items]
Common stock, shares issued (in shares) | shares		1,100,000
Collaborative Arrangement, Transaction with Party to Collaborative Arrangement | SFJ Agreement | Tranche B
Derivative [Line Items]
Common stock, shares issued (in shares) | shares		1,100,000
Collaborative Arrangement, Transaction with Party to Collaborative Arrangement | PB2452 | SFJ Agreement
Derivative [Line Items]
Initial payment received for license agreement		$ 10,000,000.0
Additional payment for license		18,400,000
Additional payment received for license agreement		71,600,000
Collaborative Arrangement, Transaction with Party to Collaborative Arrangement | PB2452 | United States Food And Drug Administration | SFJ Agreement
Derivative [Line Items]
Additional payment for license		325,000,000.0
Initial payment for license		5,000,000.0
Collaborative Arrangement, Transaction with Party to Collaborative Arrangement | PB2452 | European Medicines Agency | SFJ Agreement
Derivative [Line Items]
Additional payment for license		205,000,000.0
Initial payment for license		5,000,000.0
Collaborative Arrangement, Transaction with Party to Collaborative Arrangement | PB2452 | Pharmaceuticals And Medical Devices Agency Of Japan And National Medical Productions Administration Of China | SFJ Agreement
Derivative [Line Items]
Additional payment for license		59,000,000.0
Initial payment for license		1,000,000.0
Collaborative Arrangement, Transaction with Party to Collaborative Arrangement | PB2452 | Maximum | SFJ Agreement
Derivative [Line Items]
Potential milestones payment receivable	$ 120,000,000.0	$ 30,000,000.0