Nature of Operations and Summary of Significant Accounting Policies - Narrative (Details) - USD ($)				3 Months Ended		9 Months Ended		12 Months Ended	93 Months Ended
	May 12, 2020	Nov. 22, 2019	Nov. 02, 2018	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2013	Sep. 30, 2020	Jun. 30, 2020	Dec. 31, 2019
Initial Public Offering:
Sale of stock, price per share (USD per share)										$ 32.50
Revenue Recognition
Allowance for product returns				$ 300,000		$ 300,000			$ 300,000		$ 0
Replacement costs				0	$ 0	100,000	$ 0
Investment Securities:
Unrealized gain (loss) on investment securities				0	0	0	0
Inventory:
Finished goods inventory				23,000,000.0		23,000,000.0			23,000,000.0		7,000,000.0
Work-in-process inventory				6,100,000		6,100,000			6,100,000		1,500,000
Raw materials inventory				15,200,000		15,200,000			15,200,000		7,200,000
Inventory reserves				0		0			0		100,000
Intangible Asset:
Finite-lived intangible asset acquired								$ 1,000,000.0
Finite-lived intangible assets, weighted-average amortization period								8 years 8 months 15 days
Accumulated amortization on intangible assets				800,000		800,000			800,000		$ 700,000
Amortization of intangible assets				$ 0	$ 0	100,000	$ 100,000
Impairment of finite-lived intangible asset									$ 0
Impairment of Long-Lived Assets:
Impairment of long-lived assets						$ 0
Leases:
Weighted-average remaining lease terms for operating leases				7 years 2 months 12 days		7 years 2 months 12 days			7 years 2 months 12 days		7 years 9 months 18 days
Weighted-average discount rate on operating leases (as a percent)				6.90%		6.90%			6.90%		7.25%
Stock-Based Compensation:
Requisite service period of recognition of compensation cost						4 years
Net Loss per Share of Common Stock:
Potentially dilutive weighted-average shares not included in computation of diluted weighted average shares (in shares)				2,279,353	2,286,802	2,251,155	1,812,578
Minimum
Inventory:
Inventory shelf life						12 months
Property and Equipment:
Property and equipment useful life						3 years
Maximum
Inventory:
Inventory shelf life						27 months
Property and Equipment:
Property and equipment useful life						7 years
IPO
Initial Public Offering:
Stock issued (shares)			9,200,000
Sale of stock, price per share (USD per share)			$ 15.00
Net proceeds from sale of stock			$ 126,000,000.0
Exercise of Underwriters Option
Initial Public Offering:
Stock issued (shares)	600,000	750,000	1,200,000
Follow-on Offering
Initial Public Offering:
Stock issued (shares)	4,600,000	5,345,000
Sale of stock, price per share (USD per share)	$ 32.50	$ 22.00
Net proceeds from sale of stock	$ 140,500,000	$ 110,400,000
Common Stock
Initial Public Offering:
Conversion of preferred stock to common stock (shares)			15,813,297
Number of common stock warrants converted from preferred stock warrants (shares)			80,000
Preferred Stock
Intangible Asset:
Shares issued for purchase of intangible asset								50,000
Fair value of shares issued for purchase of intangible asset								$ 1,000,000.0
Stock Option and Restricted Stock-Based Awards
Stock-Based Compensation:
Vesting period						4 years
Restricted Stock Units
Stock-Based Compensation:
Vesting period						1 year