Customer, Supplier and Product Concentration - Percentage of the Company's Gross and Net Sales and Accounts Receivable (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Concentration Risk [Line Items]
Gross Accounts Receivable	$ 308,305				$ 378,759				$ 308,305	$ 378,759	$ 519,175
Gross sales									1,887,862	2,351,071	2,891,267
Revenues	153,386	$ 165,625	$ 190,944	$ 184,063	186,057	$ 202,428	$ 199,140	$ 253,420	694,018	841,045	1,116,843
Amerisource
Concentration Risk [Line Items]
Gross Accounts Receivable	55,160				99,771				55,160	99,771	184,623
Gross sales									386,543	554,690	852,924
Revenues									144,776	160,671	260,225
Cardinal
Concentration Risk [Line Items]
Gross Accounts Receivable	59,443				79,731				59,443	79,731	78,344
Gross sales									390,438	411,458	445,255
Revenues									109,747	150,257	182,045
McKesson
Concentration Risk [Line Items]
Gross Accounts Receivable	149,000				146,321				149,000	146,321	172,468
Gross sales									789,620	918,157	939,662
Revenues									173,363	222,715	270,276
Combined Total
Concentration Risk [Line Items]
Gross Accounts Receivable	263,603				325,823				263,603	325,823	435,435
Gross sales									1,566,601	1,884,305	2,237,841
Revenues									427,886	533,643	712,546
Other
Concentration Risk [Line Items]
Gross Accounts Receivable	$ 44,702				$ 52,936				44,702	52,936	83,740
Gross sales									321,261	466,766	653,426
Revenues									$ 266,132	$ 307,402	$ 404,297
Customer Concentration Risk | Gross Accounts Receivables
Concentration Risk [Line Items]
Customer concentration									100.00%	100.00%	100.00%
Customer Concentration Risk | Gross Sales
Concentration Risk [Line Items]
Customer concentration									100.00%	100.00%	100.00%
Customer Concentration Risk | Net Revenue
Concentration Risk [Line Items]
Customer concentration									100.00%	100.00%	100.00%
Customer Concentration Risk | Amerisource | Gross Accounts Receivables
Concentration Risk [Line Items]
Customer concentration									17.90%	26.30%	35.60%
Customer Concentration Risk | Amerisource | Gross Sales
Concentration Risk [Line Items]
Customer concentration									20.50%	23.60%	29.50%
Customer Concentration Risk | Amerisource | Net Revenue
Concentration Risk [Line Items]
Customer concentration									20.90%	19.10%	23.30%
Customer Concentration Risk | Cardinal | Gross Accounts Receivables
Concentration Risk [Line Items]
Customer concentration									19.30%	21.10%	15.10%
Customer Concentration Risk | Cardinal | Gross Sales
Concentration Risk [Line Items]
Customer concentration									20.70%	17.50%	15.40%
Customer Concentration Risk | Cardinal | Net Revenue
Concentration Risk [Line Items]
Customer concentration									15.80%	17.90%	16.30%
Customer Concentration Risk | McKesson | Gross Accounts Receivables
Concentration Risk [Line Items]
Customer concentration									48.30%	38.60%	33.20%
Customer Concentration Risk | McKesson | Gross Sales
Concentration Risk [Line Items]
Customer concentration									41.80%	39.10%	32.50%
Customer Concentration Risk | McKesson | Net Revenue
Concentration Risk [Line Items]
Customer concentration									25.00%	26.50%	24.20%
Customer Concentration Risk | Combined Total | Gross Accounts Receivables
Concentration Risk [Line Items]
Customer concentration									85.50%	86.00%	83.90%
Customer Concentration Risk | Combined Total | Gross Sales
Concentration Risk [Line Items]
Customer concentration									83.00%	80.20%	77.40%
Customer Concentration Risk | Combined Total | Net Revenue
Concentration Risk [Line Items]
Customer concentration									61.70%	63.50%	63.80%
Customer Concentration Risk | Other | Gross Accounts Receivables
Concentration Risk [Line Items]
Customer concentration									14.50%	14.00%	16.10%
Customer Concentration Risk | Other | Gross Sales
Concentration Risk [Line Items]
Customer concentration									17.00%	19.80%	22.60%
Customer Concentration Risk | Other | Net Revenue
Concentration Risk [Line Items]
Customer concentration									38.30%	36.50%	36.20%