Income Taxes - Deferred Income Taxes Components (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Deferred tax assets:
Net operating loss carryforward	$ 53,189	$ 41,086
Property & equipment	648	524
Inventory	395	58
Stock options	11,473	8,195
Intangible assets, definite-lived	40	42
General business credit	9,300	6,651
Deferred revenue	23	253
Other	24	45
Total deferred income tax assets	75,092	56,854
Valuation allowance	(63,060)	(56,854)
Deferred tax assets	12,032	0
Deferred income tax liabilities:
Debt amortization	(12,032)	0
Total deferred income tax liabilities	(12,032)	0
Net deferred income taxes	$ 0	$ 0