Significant Accounting Policies - Additional Information (Detail)	3 Months Ended	12 Months Ended
	Dec. 31, 2013 Segment	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Significant Accounting Policies [Line Items]
Allowance for doubtful accounts		$ 700,000	$ 500,000	$ 100,000	$ 100,000
Allowance for doubtful accounts, additions		500,000	400,000	0
Write-offs of uncollectible accounts		200,000	1,200	5,000
Inventory reserves		3,200,000	2,700,000	2,200,000	$ 2,200,000
Inventory reserves additions		700,000	900,000	800,000
Provision for inventory obsolescence		691,000	866,000	822,000
Impairment losses on long-lived assets		$ 0	0
Number of reportable segments | Segment	1
Standard warranty period		12 months
Product warranty accrual period		1 year
Advertising costs		$ 4,800,000	5,900,000	5,300,000
Guarantees and indemnifications liabilities		0	0
Inventory Valuation Reserve
Significant Accounting Policies [Line Items]
Provision for inventory obsolescence		$ 300,000	$ 400,000	$ 700,000
Manufacturing equipment
Significant Accounting Policies [Line Items]
Estimated useful lives of the assets		5 years
Prototype Systems
Significant Accounting Policies [Line Items]
Estimated useful lives of the assets		2 years
Computer equipment
Significant Accounting Policies [Line Items]
Estimated useful lives of the assets		3 years
Furniture and fixtures
Significant Accounting Policies [Line Items]
Estimated useful lives of the assets		5 years
Minimum
Significant Accounting Policies [Line Items]
Extended warranty period		12 months
Minimum | Lease and loaner instruments
Significant Accounting Policies [Line Items]
Estimated useful lives of the assets		1 year
Maximum
Significant Accounting Policies [Line Items]
Extended warranty period		36 months
Maximum | Lease and loaner instruments
Significant Accounting Policies [Line Items]
Estimated useful lives of the assets		5 years
Sales Revenue, Net | Customer Concentration Risk | Merck Sharp & Dohme Corp.
Significant Accounting Policies [Line Items]
Concentration Risk, Percentage			25.00%	13.00%
Sales Revenue, Net | Customer Concentration Risk | Medivation, Inc. and Astellas Pharma, Inc.
Significant Accounting Policies [Line Items]
Concentration Risk, Percentage			10.00%
Sales Revenue, Net | Customer Concentration Risk | Lam Research Corporation [Member]
Significant Accounting Policies [Line Items]
Concentration Risk, Percentage		17.00%
Accounts Receivable [Member] | Customer Concentration Risk
Significant Accounting Policies [Line Items]
Concentration Risk, Percentage			0.00%