Distribution Agreement - Additional Information (Detail) $ in Thousands	1 Months Ended		12 Months Ended
	Aug. 31, 2016 USD ($)	Dec. 31, 2014 USD ($) Installment	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Marketing Agreement [Line Items]
Distribution fee reclassified to deferred revenue			$ 23,389	$ 10,433
Distribution rights revenue			$ 475	178	$ 0
Itochu Corporation Agreement
Marketing Agreement [Line Items]
Distribution agreement term		10 years
Distribution fees		$ 4,000
Number of installments | Installment		3
Remaining term of distribution agreement	8 years 6 months		8 years 6 months
Distribution rights revenue			$ 475	$ 178
Itochu Corporation Agreement | Distribution Rights
Marketing Agreement [Line Items]
Distribution fee reclassified to deferred revenue	$ 4,000		$ 4,000
Itochu Corporation Agreement | First Installment
Marketing Agreement [Line Items]
Distribution fees		$ 1,000
Itochu Corporation Agreement | Second Installment
Marketing Agreement [Line Items]
Distribution fees		1,000
Itochu Corporation Agreement | Third Installment
Marketing Agreement [Line Items]
Distribution fees		$ 2,000
Distribution fees payment	$ 2,000
Itochu Corporation Agreement | First and Second Installment
Marketing Agreement [Line Items]
Distribution fees payment					$ 2,000	$ 2,000