Basis of Presentation and Significant Accounting Policies - Summary of Percentage of the Company's Total Net Product Revenue (Detail) - Revenue Benchmark [Member] - Customer Concentration Risk [Member]		3 Months Ended		6 Months Ended
		Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Customer A [Member]
Concentration Risk [Line Items]
Concentration risk, percentage		70.20%	65.20%	69.70%	66.30%
Customer B [Member]
Concentration Risk [Line Items]
Concentration risk, percentage	[1]	0.00%	34.80%	0.00%	33.70%
Customer C [Member]
Concentration Risk [Line Items]
Concentration risk, percentage		11.20%	0.00%	10.40%	0.00%
Customer [Member]
Concentration Risk [Line Items]
Concentration risk, percentage		81.40%	100.00%	80.10%	100.00%

[1] *During 2023, the Company sold FYCOMPA® through a Transition Service Agreement with a U.S. subsidiary of Eisai. Effective January 1, 2024, FYCOMPA® is being sold and distributed through a third-party logistics (3PL) organization. Customers B and C both relate to sales of FYCOMPA®.