Co-Promotion Agreement - Additional Information (Detail) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
Co Promotion Agreement [Line Items]
Accrued expenses and other current liabilities	$ 134,542	$ 84,171
Co-Promotion Agreement | Kowa Pharmaceuticals America, Inc.
Co Promotion Agreement [Line Items]
Agreement amended date	Jul. 25, 2017
Promotion fee as a percentage of gross margin		18.50%
Maximum co-promotion tail payments receive period	3 years
Co-promotion tail payments receivable		$ 17,800
Tail payments during the period	$ 4,800
Accrued co- promotion tail payments	12,300	$ 16,600
Accrued expenses and other current liabilities	$ 7,600