License and Collaboration Agreements - Additional Information (Detail)				1 Months Ended			3 Months Ended			6 Months Ended	9 Months Ended
	Jan. 01, 2021	Dec. 12, 2018 USD ($)	Jul. 10, 2017 USD ($)	Aug. 31, 2019 USD ($)	Nov. 30, 2018 USD ($)	Mar. 31, 2013 USD ($)	Sep. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Sep. 30, 2018 USD ($)	Dec. 31, 2018 USD ($)	Sep. 30, 2019 USD ($) Country	Sep. 30, 2018 USD ($)
Collaborative Agreements And Contracts [Line Items]
Revenue							$ 2,509,000		$ 486,000		$ 11,732,000	$ 2,129,000
Accounts receivable							8,855,000			$ 627,000	8,855,000
Amended Alimera Agreement [Member]
Collaborative Agreements And Contracts [Line Items]
Royalty percentage earned from sales of product										2.00%
Calendar year net sales threshold for increase in royalty rate		$ 75,000,000
Contingently recoverable accumulated commercialization losses			$ 25,000,000								9,200,000
Partial cancellation of contingently recoverable accumulated commercialization losses in lieu of upfront license fee			$ 10,000,000
Royalty percentage offset for amounts earned above 2% to be applied against balance of accumulated commercialization losses		50.00%
Additional cancellation of contingently recoverable commercialization losses								$ 5,000,000
Accrued sales-based royalty income							446,000		215,000		1,400,000	594,000
Revenue							475,000		249,000		1,500,000	682,000
Amended Alimera Agreement [Member] | Scenario, Forecast [Member]
Collaborative Agreements And Contracts [Line Items]
Royalty percentage offset for amounts earned above 2% to be applied against balance of accumulated commercialization losses	20.00%
Amended Alimera Agreement [Member] | Minimum [Member]
Collaborative Agreements And Contracts [Line Items]
Royalty percentage earned from sales of product		6.00%
Amended Alimera Agreement [Member] | Maximum [Member]
Collaborative Agreements And Contracts [Line Items]
Royalty percentage earned from sales of product		8.00%
Bausch and Lomb [Member]
Collaborative Agreements And Contracts [Line Items]
Accounts receivable							0		253,000		$ 0	253,000
OncoSil Medical UK Limited [Member]
Collaborative Agreements And Contracts [Line Items]
Royalty percentage earned from sales of product											8.00%
Revenue							0		0		$ 0	0
Percentage of non-royalty consideration received from sublicense											20.00%
Deferred revenue							0				$ 0
License agreement commencement date											2012-12
Receipt of upfront license fee						$ 100,000
Ocumension Therapeutics [Member]
Collaborative Agreements And Contracts [Line Items]
Deferred revenue							0				$ 0
Receipt of upfront license fee					$ 1,750,000
Potential future payments based on achievement of development and regulatory milestones											7,250,000
Potential future payments based on achievement of commercial-based milestones											3,000,000
Development milestone payment received				$ 1,000,000
Ocumension Therapeutics [Member] | Maximum [Member]
Collaborative Agreements And Contracts [Line Items]
Product supply milestones and development milestones											$ 7,250,000
ILUVIEN [Member] | Europe [Member]
Collaborative Agreements And Contracts [Line Items]
Number of countries in which lead licensed product received regulatory approval | Country											17
Royalty Income [Member]
Collaborative Agreements And Contracts [Line Items]
Revenue							446,000		430,000		$ 1,666,000	1,331,000
Royalty Income [Member] | Bausch and Lomb [Member]
Collaborative Agreements And Contracts [Line Items]
Revenue							0		215,000		204,000	737,000
Collaborative Research and Development [Member] | OncoSil Medical UK Limited [Member]
Collaborative Agreements And Contracts [Line Items]
Revenue										$ 100,000
Collaborative Research and Development [Member] | Feasibility Study Agreement [Member]
Collaborative Agreements And Contracts [Line Items]
Revenue							0		15,000		0	700,000
Deferred revenue							0				0
Product [Member]
Collaborative Agreements And Contracts [Line Items]
Revenue							1,009,000		0		8,941,000	0
Product [Member] | Ocumension Therapeutics [Member]
Collaborative Agreements And Contracts [Line Items]
Revenue							53,000				53,000
License and Collaboration Agreement [Member]
Collaborative Agreements And Contracts [Line Items]
Revenue							1,054,000		$ 56,000		1,125,000	$ 798,000
License and Collaboration Agreement [Member] | Ocumension Therapeutics [Member]
Collaborative Agreements And Contracts [Line Items]
Revenue							$ 0				$ 30,000