Revenues, Significant Customers and Concentrations of Risk - Summary of Significant Customers from which the Company Derived 10% or More of Total Revenue (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Concentration Risk [Line Items]
Total revenues	$ 23,286	$ 12,703
Teva [Member]
Concentration Risk [Line Items]
Total revenues	10,611	4,167
AMAG [Member]
Concentration Risk [Line Items]
Total revenues	4,592	2,834
McKesson [Member]
Concentration Risk [Line Items]
Total revenues	1,247	1,843
AmerisourceBergen [Member]
Concentration Risk [Line Items]
Total revenues	1,581	1,423
Ferring [Member]
Concentration Risk [Line Items]
Total revenues	$ 3,096	$ 1,474