Segment Information - Significant Customers (Details) - Credit Concentration Risk	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Revenues, Gross | McKesson Corporation
Concentration Risk [Line Items]
Concentration risk percentage (less than for CVS/Caremark 2017 revenue)	17.00%	14.00%	10.00%
Revenues, Gross | Walgreen Co.
Concentration Risk [Line Items]
Concentration risk percentage (less than for CVS/Caremark 2017 revenue)	15.00%	20.00%	17.00%
Revenues, Gross | Accredo/Curascript
Concentration Risk [Line Items]
Concentration risk percentage (less than for CVS/Caremark 2017 revenue)	14.00%	14.00%	14.00%
Accounts Receivable | McKesson Corporation
Concentration Risk [Line Items]
Concentration risk percentage (less than for CVS/Caremark 2017 revenue)	22.00%	16.00%
Accounts Receivable | Walgreen Co.
Concentration Risk [Line Items]
Concentration risk percentage (less than for CVS/Caremark 2017 revenue)	14.00%	16.00%
Accounts Receivable | Accredo/Curascript
Concentration Risk [Line Items]
Concentration risk percentage (less than for CVS/Caremark 2017 revenue)	15.00%	10.00%