Company and Nature of Business - Additional Information (Details) - USD ($)					1 Months Ended					3 Months Ended		9 Months Ended
	Aug. 03, 2020	May 08, 2020	Mar. 27, 2020	Jan. 21, 2020	Sep. 30, 2020	Jul. 31, 2020	Mar. 31, 2020	Jan. 31, 2020	Jul. 31, 2019	Sep. 30, 2020	Jun. 30, 2020	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Cash flow from operations												$ (22,265,000)	$ (24,912,000)
Accumulated deficit					$ 271,034,000					$ 271,034,000		271,034,000		$ 248,630,000
Proceeds from private offering of common stock					$ 2,000,000	$ 4,000,000		$ 7,500,000	$ 13,800,000			11,475,000	$ 13,800,000
Proceeds from capital contribution			$ 11,500,000
PPP Loan
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Debt instrument interest rate		1.00%
Debenture maturity date		May 08, 2022
Amount of loan received		$ 1,133,600
PPP Loan | Five Star Bank
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Amount of loan received		$ 1,100
Alzheimers Association
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Sale of stock, consideration received												750,000
Proceeds from the sale of shares												575,000,000
Open Market Sale Agreement
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Proceeds from the sale of shares										$ 12,300,000	$ 1,200,000
Open Market Sale Agreement | Common Stock
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Number of common stock sold										3,815,600	317,688
Securities Purchase Agreement
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Sale of stock, consideration received										$ 26,600,000
Debt instrument interest rate	7.00%
Debt instrument principal amount	$ 8,640,000
Purchase price of convertible debentures	$ 8,000,000
Debt instrument, discount rate	8.00%
Debenture maturity date	Aug. 03, 2021
Common stock conversion price	$ 9.4125
Stock Purchase Agreement | Keystone Capital Partners, LLC
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Stock purchase program number of shares agree to purchase												5,000,000
Proceeds from the sale of shares											$ 1,200,000	$ 300,000
Stock Purchase Agreement | Common Stock
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Number of common stock sold				1,468,563
Stock Purchase Agreement | Common Stock | Keystone Capital Partners, LLC
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Number of common stock sold											324,424	47,319
Maximum
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Sale of stock, consideration received												$ 113,000,000
Maximum | Stock Purchase Agreement | Common Stock | Keystone Capital Partners, LLC
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Proceeds from the sale of shares							$ 5,000,000