Commitments and Contingencies - Narrative (Details)		1 Months Ended	3 Months Ended		9 Months Ended		39 Months Ended
	Mar. 16, 2020 petition	Sep. 30, 2020 USD ($) petition	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Dec. 31, 2023 USD ($)	Aug. 31, 2020 ft²	Dec. 31, 2019 USD ($)	Jun. 30, 2019 ft²	Nov. 30, 2017 ft²	Aug. 31, 2014 ft²
Loss Contingencies [Line Items]
Variable lease cost			$ 65,000	$ 55,000	$ 123,000	$ 98,000
Right-of-use assets obtained in exchange for operating lease liabilities			0	0	3,000,000.0	1,500,000
Right-of-use asset		$ 6,600,000	6,600,000		6,600,000				$ 4,200,000
Cash paid for operating lease liabilities			400,000	300,000	1,000,000.0	700,000
Amortization of the ROU asset			$ 200,000	200,000	$ 600,000	300,000
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%
Period after first sale royalty is due					12 years
Net revenue due as royalty (as a percent)					4.00%
Revenues			$ 35,243,000	1,309,000	$ 76,752,000	3,874,000
Royalty expense			1,400,000	$ 100,000	3,000,000.0	$ 200,000
Accrued royalty expense		$ 1,400,000	1,400,000		1,400,000				$ 400,000
Medtronic Patents | Pending Litigation
Loss Contingencies [Line Items]
Petitions filed regarding patents allegedly infringed upon | petition	7
Gain Contingency, Patents Allegedly Infringed upon, Number Accepted/ Instituted | petition		6
Maximum
Loss Contingencies [Line Items]
Royalty commitments		$ 200,000	$ 200,000		$ 200,000
First Lease
Loss Contingencies [Line Items]
Term of operating lease contract												5 years
Net rentable area (square feet) | ft²												12,215
Second Lease
Loss Contingencies [Line Items]
Term of operating lease contract											7 years
Net rentable area (square feet) | ft²											25,548
Renewal term of operating lease											5 years
Third Lease
Loss Contingencies [Line Items]
Term of operating lease contract										8 years
Net rentable area (square feet) | ft²										32,621
Renewal term of operating lease										5 years
Fourth Lease
Loss Contingencies [Line Items]
Term of operating lease contract								38 months
Net rentable area (square feet) | ft²								5,693
Fourth Lease | Forecast
Loss Contingencies [Line Items]
Operating lease rent expense							$ 300,000
Variable lease cost							$ 100,000