Summary of Significant Accounting Policies - Chargebacks, Rebates, Administrative Fees and Other, and Sales Returns (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Accounting Policies [Abstract]
Chargeback provision	$ 236,701	$ 347,106	$ 754,137	$ 856,699
Sales chargebacks as percentage of gross sales	40.40%	44.10%
Gross sales	$ 586,351	$ 787,808	$ 1,833,998	2,089,567
Change in ratio of direct to indirect sales for chargeback reserves used in sensitivity analysis	4.70%		4.70%
Potential increase in chargeback expense based on sensitivity analysis	$ 500		$ 500
Potential decrease in chargeback expense based on sensitivity analysis	2,700		2,700
Rebates, administrative and other fees	$ 127,904	$ 130,429	$ 362,042	321,718
Rebates, administrative and other fees as a percentage of gross sales	21.80%	16.60%
Change in ratio of direct to indirect sales for rebates, administrative and other fees used in sensitivity analysis	4.70%		4.70%
Potential increase in rebates, administrative and other fees expense based on sensitivity analysis	$ 100		$ 100
Potential decrease in rebates, administrative and other fees expense based on sensitivity analysis	1,500		1,500
Sales returns	$ 6,187	$ 7,970	$ 22,721	$ 31,056
Change in ratio of direct to indirect sales for sales return reserve used in sensitivity analysis	1.10%	1.00%
Change in lag time to process returns for sales returns reserve used in sensitivity analysis			1 month
Potential decrease in sales returns expense based on sensitivity analysis	$ 900		$ 900
Potential increase in sales returns expense based on sensitivity analysis	$ 500		$ 500
Accounts, Notes, Loans and Financing Receivable [Line Items]
Extended chargeback period			84 days
Minimum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Standard chargeback period			28 days
Maximum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Standard chargeback period			42 days