Accrued Expenses (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Accrued Expenses
Employee compensation expenses	$ 2,911	$ 5,293
Sales discounts and allowances	10,243	2,650
Selling and marketing expenses	808	453
Research and development expenses	3,294	1,437
Professional fees	1,276	1,123
Other	2,254	1,030
Total accrued expenses	$ 20,786	$ 11,986