Accrued Sales Deductions (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Accrued Sales Deductions
Accrued rebates	$ 66,742	$ 49,460
Accrued product returns	19,228	18,883
Accrued sales deductions, net	$ 85,970	$ 68,343