Summary of Significant Accounting Policies - Additional Information (Detail)	3 Months Ended		12 Months Ended
	Mar. 31, 2019 USD ($) Customer Segment	Mar. 31, 2018 USD ($)	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
Revenue recognized, that were included in deferred product revenue	$ 200,000
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		2
Protracted length of inventory	1 year
Inventory valuation reserves	$ 400,000		$ 300,000
Accumulated amortization intangible assets	$ 1,700,000		1,700,000
Estimated useful life of intangible assets	10 years
Number of reportable segments | Segment	1
Impairment charges acquired intangible asstes	$ 0	$ 0
Period of warranty	1 year
Warranty claim liability	$ 0		$ 0
Operating lease right-of-use assets	15,631,000
Operating lease liabilities – current	1,560,000
Operating lease liabilities – non-current	$ 19,311,000
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	59.00%		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