Gross-to-Net Product Sales and Significant Customers - Summary of Customers Representing 10% or More of Gross Product Sales (Details) - Product [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenue, Major Customer [Line Items]
Gross product sales	$ 190,825	$ 245,797	$ 244,770
McKesson Corporation and its affiliates [Member]
Revenue, Major Customer [Line Items]
Gross product sales	69,320	76,363	75,952
AmerisourceBergen Corporation, and its affiliates [Member]
Revenue, Major Customer [Line Items]
Gross product sales	55,576	79,362	93,951
Cardinal Health, Inc. and its affiliates [Member]
Revenue, Major Customer [Line Items]
Gross product sales	42,074	64,634	58,780
All Other Customers [Member]
Revenue, Major Customer [Line Items]
Gross product sales	$ 23,855	$ 25,438	$ 16,087
Customer Concentration Risk [Member] | Gross Product Sales [Member]
Revenue, Major Customer [Line Items]
Percentage of sales	100.00%	100.00%	100.00%
Customer Concentration Risk [Member] | Gross Product Sales [Member] | McKesson Corporation and its affiliates [Member]
Revenue, Major Customer [Line Items]
Percentage of sales	36.30%	31.10%	31.00%
Customer Concentration Risk [Member] | Gross Product Sales [Member] | AmerisourceBergen Corporation, and its affiliates [Member]
Revenue, Major Customer [Line Items]
Percentage of sales	29.10%	32.30%	38.40%
Customer Concentration Risk [Member] | Gross Product Sales [Member] | Cardinal Health, Inc. and its affiliates [Member]
Revenue, Major Customer [Line Items]
Percentage of sales	22.00%	26.30%	24.00%
Customer Concentration Risk [Member] | Gross Product Sales [Member] | All Other Customers [Member]
Revenue, Major Customer [Line Items]
Percentage of sales	12.50%	10.30%	6.60%