Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($)		1 Months Ended	12 Months Ended
	Aug. 31, 2016	Aug. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jan. 01, 2019	Dec. 31, 2015
Significant Accounting Policies [Line Items]
Restricted cash			$ 1,933,000	$ 1,143,000
Allowance for doubtful accounts			0	0
Inventory lower of cost and net realizable value adjustment			340,000	911,000	$ 1,939,000
Asset retirement obligation			192,000
Impairment loss recognized			$ 0	0	0
Service contract term			12 months
Long-term trade receivables			$ 400,000	0
Long-term trade credit maintenance services term			1 year
Deferred revenue, recognized			$ 19,900,000	6,600,000	600,000
Deferred commission			3,900,000	3,500,000
Penalties and interest related to income taxes			$ 0
Right-of-use assets, operating lease						$ 11,900,000
Lease liabilities, operating lease						$ 12,600,000
ASU No. 2016-18
Significant Accounting Policies [Line Items]
Increase in cash, cash equivalents and restricted cash				1,100,000	1,100,000		$ 900,000
Itochu Corporation Agreement
Significant Accounting Policies [Line Items]
Remaining term of distribution agreement	8 years 6 months	8 years 6 months	8 years 6 months
Itochu Corporation Agreement | Distribution Rights
Significant Accounting Policies [Line Items]
Distribution revenue reclassified as deferred revenue	$ 4,000,000	$ 4,000,000	$ 4,000,000
Asset Retirement Obligation
Significant Accounting Policies [Line Items]
Accretion expenses			$ 33,000	40,000	$ 36,000
Software
Significant Accounting Policies [Line Items]
Property and equipment, useful life			3 years
Minimum
Significant Accounting Policies [Line Items]
Property and equipment, useful life			2 years
Expected long-term trade receivables collection period			3 years
Maximum
Significant Accounting Policies [Line Items]
Property and equipment, useful life			15 years
Expected long-term trade receivables collection period			4 years
Irrevocable Standby Letters of Credit
Significant Accounting Policies [Line Items]
Letters of credit drawn, amount			$ 0	0
Collateral for Letters of Credit
Significant Accounting Policies [Line Items]
Restricted cash			900,000	900,000
Collateral For Credit Card
Significant Accounting Policies [Line Items]
Restricted cash			$ 1,000,000	$ 200,000