Summary of Significant Accounting Principles - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2015 USD ($) segment customer	Dec. 31, 2014 USD ($) customer	Dec. 31, 2013 USD ($)	Dec. 31, 2012 USD ($)
Significant Accounting Policies [Line Items]
Cash and cash equivalents | $	$ 64,501,000	$ 375,937,000	$ 61,011,000	$ 37,171,000
Maximum days MYALEPT can be held as inventory	21 days
Amount of material uncertain tax positions | $	$ 0	$ 0
Number of business segment in which company currently operating | segment	1
Customer Concentration Risk [Member] | Sales Revenue, Net [Member]
Significant Accounting Policies [Line Items]
Number of major customer accounted for net sale and accounts receivable | customer	1	0
Customer Concentration Risk [Member] | Accounts Receivable [Member]
Significant Accounting Policies [Line Items]
Number of major customer accounted for net sale and accounts receivable | customer	1	1
Accounts receivable, percentage	17.00%	12.00%