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Commitments and Contingencies - Additional Information (Details) - USD ($)	1 Months Ended		12 Months Ended
	Sep. 30, 2015	Oct. 31, 2014	Dec. 31, 2020	Dec. 31, 2019
Loss Contingencies [Line Items]
Rent expense			$ 732,000	$ 696,000
Operating expenses			29,832,000	37,502,000
Accounts payable			2,513,000	4,636,000
JHU
Loss Contingencies [Line Items]
Operating expenses			203,000	395,000
License Agreement | JHU
Loss Contingencies [Line Items]
One-time, non-refundable fee	$ 100,000
Maximum credit percentage of running royalty rate	50.00%
Kala Agreement
Loss Contingencies [Line Items]
Percentage of minimum annual royalties including development milestone payments for first licensed product		25.00%
Development milestone payment extension period		1 year
Development milestone payable under second licensed product		$ 100,000
Development milestone payable under third licensed product		$ 150,000
Operating expenses			0	0
Accounts payable			0	0
AffaMed Letter
Loss Contingencies [Line Items]
Operating expenses			0	0
Accounts payable			$ 0	$ 0
Option expiration period			Jul. 31, 2021
Collaborative arrangement, description			The AffaMed Letter provides AffaMed with an initial 30-day period to propose terms for such a license which, if such terms are approved by a majority of the Company’s board of directors (excluding the director originally appointed by AffaMed and who continues to serve on our board), shall lead to a 60-day exclusive negotiation period. During this period of up to 90 days, the Company is prohibited from soliciting, initiating, encouraging or assisting the submission of any other proposal, negotiation or offer for the development, registration and commercialization of GB-102 in China, Hong Kong, Taiwan, Macau or South Korea.
Redwood City, California
Loss Contingencies [Line Items]
Operating lease, term			2021-08
Baltimore, Maryland
Loss Contingencies [Line Items]
Operating lease, term			2023-06
United States | Kala Agreement
Loss Contingencies [Line Items]
Percentage of commercial milestone payments reduced		50.00%
Minimum | License Agreement | JHU
Loss Contingencies [Line Items]
Percentage of royalty payments on net sales	50.00%
Percentage of developmental milestone payment for second and third products	50.00%
Maximum | License Agreement | JHU
Loss Contingencies [Line Items]
Aggregate total amount of developmental milestone payment	$ 2,000,000
Research and Development
Loss Contingencies [Line Items]
Contractual obligation			$ 7,700,000
Research and Development | Minimum
Loss Contingencies [Line Items]
Contractual obligation term			3 months
Research and Development | Maximum
Loss Contingencies [Line Items]
Contractual obligation term			15 months

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