Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($)		3 Months Ended		9 Months Ended
	Aug. 31, 2016	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Jan. 01, 2018	Dec. 31, 2017
Significant Accounting Policies [Line Items]
Long-term trade receivables		$ 400,000		$ 400,000			$ 0
Long-term trade credit maintenance services term				1 year
Allowance for doubtful accounts		0		$ 0			$ 0
Deferred revenue, recognized		12,200,000	$ 9,000,000	18,300,000	$ 5,800,000
Operating leases future minimum payments due		$ 16,245,000		$ 16,245,000
ASU No. 2016-18
Significant Accounting Policies [Line Items]
Increase in cash, cash equivalents and restricted cash						$ 1,100,000
Minimum
Significant Accounting Policies [Line Items]
Expected long-term trade receivables collection period				3 years
Maximum
Significant Accounting Policies [Line Items]
Expected long-term trade receivables collection period				4 years
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