Summary of Significant Accounting Policies - Additional Information (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2021 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2021 USD ($) Segment	Sep. 30, 2020 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Summary Of Significant Accounting Policies [Line Items]
Number of reporting segment | Segment			1
Number of reporting units | Segment			3
Maturity period of highly liquid investments with original maturities			90 days
Cash, cash equivalents and restricted cash balance	$ 70,588,000	$ 140,868,000	$ 70,588,000	$ 140,868,000	$ 115,536,000	$ 73,507,000
Estimated useful life for certain of its demonstration, placement and evaluation units	5 years		7 years
Standard product warranty period			1 year
Standard payment term to customer			30 days
Revenue, performance obligation, description of payment terms	When determining the transaction price of a contract, an adjustment is made if payment from a customer occurs either significantly before or significantly after performance, resulting in a significant financing component. Applying a practical expedient under ASC 606, the Company does not assess whether a significant financing component exists if the period between when the Company performs its obligations under the contract and when the customer pays is one year or less.
Revenue, remaining performance obligation, amount	$ 0	0	$ 0	$ 0
Dividend yield assumed			0.00%	0.00%
Provision or benefit for income taxes	0	0	$ 0	$ 0
Shipping and Handling
Summary Of Significant Accounting Policies [Line Items]
Shipping and handling costs	800,000	$ 600,000	1,500,000	$ 1,700,000
Prepaid Expenses and Other Current Assets
Summary Of Significant Accounting Policies [Line Items]
Current value of future lease payments	1,200,000		1,200,000		2,700,000
Outside U.S.
Summary Of Significant Accounting Policies [Line Items]
Long-term assets	2,100,000		2,100,000		1,700,000
Cash, cash equivalents and restricted cash balance	$ 1,100,000		$ 1,100,000		$ 400,000