Summary of Significant Accounting Policies - Additional Information (Detail)	3 Months Ended			6 Months Ended		12 Months Ended
	Jun. 30, 2019 USD ($) Customer	Mar. 31, 2019 Segment	Jun. 30, 2018 USD ($)	Jun. 30, 2019 USD ($) Customer	Jun. 30, 2018 USD ($)	Dec. 31, 2018 USD ($) Customer	Jan. 01, 2019 USD ($)
Summary Of Significant Accounting Policies [Line Items]
Description of payment of customer invoice contract				The Company invoices its customers based upon the terms in the contracts, which is generally from 30 to 60 days.
Contract asset	$ 0			$ 0		$ 0
Revenue recognized, that were included in deferred product revenue				$ 400,000
Application of an optional exemption not to disclose the value of unsatisfied performance obligations				true
Number of major customers representing outstanding trade receivables | Customer	3			3		2
Protracted length of inventory				1 year
Inventory valuation reserves	$ 300,000			$ 300,000		$ 300,000
Non-cash purchases of capital expenditures				2,900,000	$ 400,000
Accumulated amortization intangible assets	1,800,000			1,800,000		1,700,000
Estimated useful life of intangible assets		10 years
Number of reportable segments | Segment		1
Impairment charges acquired intangible asstes	0		$ 0	$ 0	$ 0
Period of warranty				1 year
Warranty claim liability	0			$ 0		$ 0
Operating lease right-of-use assets	14,417,000			14,417,000
Operating lease liabilities – current	1,711,000			1,711,000
Operating lease liabilities – non-current	$ 18,722,000			$ 18,722,000
ASU 2016-02
Summary Of Significant Accounting Policies [Line Items]
Operating lease right-of-use assets							$ 2,400,000
Operating lease liabilities – current							2,400,000
Operating lease liabilities – non-current							$ 2,400,000
Trade Accounts Receivable | Customer Concentration Risk
Summary Of Significant Accounting Policies [Line Items]
Concentration risk, percentage				58.00%		50.00%
Minimum
Summary Of Significant Accounting Policies [Line Items]
Payment of customer invoice contract period				30 days
Shelf lives of inventory				18 months
Estimated useful life of property and equipment				3 years
Maximum
Summary Of Significant Accounting Policies [Line Items]
Payment of customer invoice contract period				60 days
Shelf lives of inventory				24 months
Estimated useful life of property and equipment				5 years