Balance Sheet Components - Additional Information (Detail) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2018	Dec. 31, 2017
Inventory [Line Items]
Prepaid and other long-term assets	$ 9,645	$ 9,645	$ 0
Charge for reserve on obsolescence of inventories		2,246
Estimated reserve for obsolescence of inventories	2,200	2,200
Charge associated with our Gen 1 manufacturing process transition	10,300	10,311
Write-down of cost basis of inventory on hand	4,600
Prepaid manufacturing	2,900
Accrued liability on minimum purchase commitment	2,800
Prepaid manufacturing	0	0	2,300
Long-term prepaid manufacturing	$ 10,894	10,894	$ 9,600
Cost of Sales
Inventory [Line Items]
Charge for reserve on obsolescence of inventories		$ 2,200