Customer, Supplier and Product Concentration - Disaggregation of Revenue by Customer (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Concentration Risk [Line Items]
Revenues, net	$ 190,944	$ 199,140	$ 375,007	$ 452,560
Net Revenue | Customer Concentration Risk
Concentration Risk [Line Items]
Concentration risk percentage	100.00%	100.00%	100.00%	100.00%
Big 3 Wholesalers combined
Concentration Risk [Line Items]
Revenues, net	$ 112,245	$ 123,663	$ 230,611	$ 286,279
Big 3 Wholesalers combined | Net Revenue | Customer Concentration Risk
Concentration Risk [Line Items]
Concentration risk percentage	58.80%	62.10%	61.50%	63.30%
Amerisource
Concentration Risk [Line Items]
Revenues, net	$ 39,256	$ 39,654	$ 77,211	$ 83,591
Amerisource | Net Revenue | Customer Concentration Risk
Concentration Risk [Line Items]
Concentration risk percentage	20.60%	19.90%	20.60%	18.50%
Cardinal
Concentration Risk [Line Items]
Revenues, net	$ 29,861	$ 33,260	$ 57,051	$ 82,228
Cardinal | Net Revenue | Customer Concentration Risk
Concentration Risk [Line Items]
Concentration risk percentage	15.60%	16.70%	15.20%	18.20%
McKesson
Concentration Risk [Line Items]
Revenues, net	$ 43,128	$ 50,749	$ 96,349	$ 120,460
McKesson | Net Revenue | Customer Concentration Risk
Concentration Risk [Line Items]
Concentration risk percentage	22.60%	25.50%	25.70%	26.60%
All Others
Concentration Risk [Line Items]
Revenues, net	$ 78,699	$ 75,477	$ 144,396	$ 166,281
All Others | Net Revenue | Customer Concentration Risk
Concentration Risk [Line Items]
Concentration risk percentage	41.20%	37.90%	38.50%	36.70%