Summary of Significant Accounting Policies - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2017 USD ($) Customer	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	May 02, 2017 USD ($)
Summary Of Significant Accounting Policies [Line Items]
Accounts written off	$ 0
Long-term restricted cash	600,000	$ 480,000
Carrying value of debt issuance costs reported in prepaid expenses and other current assets	4,111,729	100,760
Amortization of debt issuance costs recognized as interest expense	$ 356,852	36,607	$ 41,103
Number of major customers | Customer	2
Number of customers accounted for more than 10% of accounts receivable | Customer	0
Number of customers accounted for more than 10% of net product revenue | Customer	0
2024 Convertible Notes [Member]
Summary Of Significant Accounting Policies [Line Items]
Convertible Notes, face value				$ 201,300,000
Estimated fair value of Convertible Notes	$ 248,900,000
Customer Concentration Risk | Accounts Receivable [Member]
Summary Of Significant Accounting Policies [Line Items]
Concentration risk, percentage	94.00%
Customer Concentration Risk | Total Revenue [Member]
Summary Of Significant Accounting Policies [Line Items]
Concentration risk, percentage	94.00%
Construction-in Progress [Member]
Summary Of Significant Accounting Policies [Line Items]
Property and equipment estimated useful life	7 years
Letter of Credit [Member]
Summary Of Significant Accounting Policies [Line Items]
Long-term restricted cash		50,000
Certificates of Deposit [Member]
Summary Of Significant Accounting Policies [Line Items]
Long-term restricted cash		30,000
Commercial Bank [Member]
Summary Of Significant Accounting Policies [Line Items]
Long-term restricted cash	$ 600,000	$ 400,000
Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Trade Payment Term	1 year