Balance Sheet Components - Additional Information (Detail) - USD ($)	3 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Inventory [Line Items]
Net losses incurred on valuation of inventories or write-off	$ 0
Prepaid Expenses and Other Current Assets
Inventory [Line Items]
Prepayment for purchase of inventory	8,200,000	$ 2,300,000
Prepaid And Other Long-term Assets
Inventory [Line Items]
Prepayment for purchase of inventory	4,800,000	$ 9,600,000
Andexxa
Inventory [Line Items]
Amounts capitalized as inventory	$ 0