Revenues, Significant Customers and Concentrations of Risk - Summary of Significant Customers from which the Company Derived 10% or More of Total Revenue (Detail) - Customer Concentration Risk [Member]

3 Months Ended

9 Months Ended

Sep. 30, 2020

Sep. 30, 2019

Sep. 30, 2020

Sep. 30, 2019

Teva [Member]

Concentration Risk [Line Items]

Total revenue by customer, percentage

45.00%

41.00%

42.00%

43.00%

AMAG [Member]

Concentration Risk [Line Items]

Total revenue by customer, percentage

20.00%

10.00%

19.00%

AMAG [Member] | Maximum [Member]

Concentration Risk [Line Items]

Total revenue by customer, percentage

10.00%

AmerisourceBergen Corporation [Member]

Concentration Risk [Line Items]

Total revenue by customer, percentage

11.00%

10.00%

12.00%

AmerisourceBergen Corporation [Member] | Maximum [Member]

Concentration Risk [Line Items]

Total revenue by customer, percentage

10.00%

McKesson Corporation [Member]

Concentration Risk [Line Items]

Total revenue by customer, percentage

12.00%

McKesson Corporation [Member] | Maximum [Member]

Concentration Risk [Line Items]

Total revenue by customer, percentage

10.00%

Cardinal Health [Member]

Concentration Risk [Line Items]

Total revenue by customer, percentage

11.00%

Cardinal Health [Member] | Maximum [Member]

Concentration Risk [Line Items]

Total revenue by customer, percentage

10.00%