Summary of Significant Accounting Policies - Chargebacks, Rebates, Administrative Fees and Other, and Sales Returns (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Accounting Policies [Abstract]
Payment terms period	90 days
Restricted cash	$ 2,372	$ 2,505	$ 1,800
Chargeback provision	$ 223,963	$ 280,160
Sales chargebacks as percentage of gross sales	43.00%	41.20%
Gross sales	$ 520,533	$ 680,534
Change in ratio of direct to indirect sales for chargeback reserves used in sensitivity analysis	4.90%
Potential increase in chargeback expense based on sensitivity analysis	$ 400
Potential decrease in chargeback expense based on sensitivity analysis	2,500
Rebates, administrative and other fees	$ 92,279	$ 124,378
Rebates, administrative and other fees as a percentage of gross sales	17.70%	18.30%
Change in ratio of direct to indirect sales for rebates, administrative and other fees used in sensitivity analysis	4.90%
Potential increase in rebates, administrative and other fees expense based on sensitivity analysis	$ 0
Potential decrease in rebates, administrative and other fees expense based on sensitivity analysis	700
Sales returns	$ 7,121	$ 8,418
Change in ratio of direct to indirect sales for sales return reserve used in sensitivity analysis	1.40%	1.20%
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	$ 2,800
Potential increase in sales returns expense based on sensitivity analysis	$ 2,400
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