Income Taxes - Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Deferred Tax Assets:
Accrued expenses	$ 3,572	$ 2,404
Deferred revenue	13,719	16,311
Sales return and allowances	2,296	2,157
Accrued settlement costs	2,689	0
Research and development and other tax credits	2,326	1,216
Net operating loss	3,118	1,025
Share-based compensation	3,425	4,895
Other	971	342
Deferred Tax Liabilities:
Prepaid expenses	(1,823)	(344)
Property and equipment	(2,519)	(1,555)
Intangible assets	(443)	(356)
Net Deferred Tax Assets
Net Deferred Tax Assets	27,331	26,095
Less: Valuation allowance	(27,331)	(554)	$ (554)
Net Deferred Tax Assets after Valuation Allowance	$ 0	$ 25,541