Income Taxes - Components of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Deferred tax assets:
Net operating loss carryforwards	$ 110,130	$ 101,423
Accrued expenses	7,475	5,617
Tax credits	12,540	11,826
Bad debt	104	78
Inventory	4,821	2,160
Capitalized research and development	17,931	16,079
Deferred compensation	2,669	2,535
Other	1,174	1,099
Deferred tax asset	156,844	140,817
Valuation allowance	(135,216)	(118,551)
Total deferred tax assets	21,628	22,266
Deferred tax liabilities:
Depreciation and amortization	(8,034)	(8,961)
Convertible debt	(4,149)	(3,740)
Other	0	0
Total deferred tax liabilities	(21,778)	(22,467)
Net deferred tax liability	(150)	(201)
Trademarks and trade names
Deferred tax liabilities:
Intangible assets	(765)	(733)
Developed technology and trademark
Deferred tax liabilities:
Intangible assets	$ (8,830)	$ (9,033)