Revenue, Credit Concentrations and Geographic Information - Additional Information (Detail) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2018 USD ($) Segment Customer	Dec. 31, 2017 USD ($) Customer
Concentration Risk And Geographic Information [Line Items]
Number of operating business segment | Segment	1
Accounts receivable, net	$ 384,343	$ 261,365	[1]
Largest Customers
Concentration Risk And Geographic Information [Line Items]
Accounts receivable, net	$ 86,900	$ 18,100
Accounts Receivable | Largest Customers
Concentration Risk And Geographic Information [Line Items]
Number of customers accounted for largest balance in accounts receivable | Customer	3	2
Geographic Concentration Risk | Net Product Revenue | Minimum
Concentration Risk And Geographic Information [Line Items]
Concentration risk, percentage	10.00%
Credit Concentration Risk | Accounts Receivable | Larger Customer One
Concentration Risk And Geographic Information [Line Items]
Concentration risk, percentage	29.00%	21.00%
Credit Concentration Risk | Accounts Receivable | Larger Customer Two
Concentration Risk And Geographic Information [Line Items]
Concentration risk, percentage	13.00%	18.00%

[1] December 31, 2017 balances were derived from the audited Consolidated Financial Statements included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2017, filed with the SEC on February 26, 2018.