Summary of Significant Accounting Policies - Liquidity (Details) shares in Millions			1 Months Ended				3 Months Ended						9 Months Ended		12 Months Ended
	Oct. 16, 2020 USD ($) item	Aug. 10, 2020 USD ($) shares	Aug. 31, 2020 USD ($)	Feb. 29, 2020 USD ($)	Oct. 31, 2019 USD ($)	Oct. 31, 2018 USD ($)	Sep. 30, 2020 USD ($)	Jun. 30, 2020 USD ($)	Mar. 31, 2020 USD ($)	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Significant Accounting Policies [Line Items]
Cash and cash equivalents							$ 58,722,000			$ 85,866,000			$ 58,722,000	$ 85,866,000	$ 43,531,000	$ 95,615,000
Long-term Debt.							43,200,000						43,200,000
Remaining amount available to borrow							0.0						0.0		0.0
Aggregate minimum liquidity balance													10,000,000.0		10,000,000.0
Aggregate minimum liquidity balance at quarter end													20,000,000.0		20,000,000.0
Shares issued and sold | shares		4
Issuance of common stock, net of offering costs		$ 32,900,000					32,867,000
Repayment of outstanding debt		$ 10,800,000			$ 28,900,000	$ 41,400,000							10,846,000
Net losses							15,262,000	$ (1,114,000)	$ 20,145,000	$ 26,196,000	$ 7,748,000	$ 5,275,000	34,293,000	39,219,000
Operating cash flows													(4,052,000)	(5,572,000)
Purchases of property and equipment													4,777,000	3,900,000
Expected annual savings				$ 8,000,000.0
Net cash used in operating activities													$ (4,052,000)	(5,572,000)
Term Loan Due In 2023 [Member]
Significant Accounting Policies [Line Items]
Quarterly pricipal payment amount	$ 875,000
Minimum liquidity balance	$ 20,000,000.0
Minimum subscription count, initial period | item	300,000
Minimum subscription count, subsequent period | item	320,000
LIBOR
Significant Accounting Policies [Line Items]
Margin added to variable rate (as a percent)													1.00%
LIBOR | Term Loan Due In 2023 [Member]
Significant Accounting Policies [Line Items]
Margin added to variable rate (as a percent)	8.00%
LIBOR | Term Loan Due In 2023 [Member] | Minimum
Significant Accounting Policies [Line Items]
Interest rate (as a percent)	1.50%
Subsequent Event | Term Loan Due In 2023 [Member]
Significant Accounting Policies [Line Items]
Face value of debt	$ 35,000,000.0
Quarterly pricipal payment amount	875,000
Minimum liquidity balance	$ 20,000,000.0
Minimum subscription count, initial period | item	300,000
Minimum subscription count, subsequent period | item	320,000
Subsequent Event | LIBOR | Term Loan Due In 2023 [Member]
Significant Accounting Policies [Line Items]
Margin added to variable rate (as a percent)	8.00%
Subsequent Event | LIBOR | Term Loan Due In 2023 [Member] | Minimum
Significant Accounting Policies [Line Items]
Interest rate (as a percent)	1.50%
Revision of Prior Period, Accounting Standards Update, Adjustment [Member]
Significant Accounting Policies [Line Items]
Operating cash flows														(300,000)
Net cash used in operating activities														$ (300,000)
Letter of credit
Significant Accounting Policies [Line Items]
Outstanding borrowings in long term debt							300,000						$ 300,000		300,000
Revolving credit facility
Significant Accounting Policies [Line Items]
Outstanding borrowings in long term debt							$ 43,832,000						$ 43,832,000		$ 54,678,000
Repayment of outstanding debt			$ 10,800,000