Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
CASH FLOWS FROM OPERATING ACTIVITIES
Net loss	$ (32,798)	$ (71,348)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock based compensation expense	5,963	23,932
Depreciation and amortization	2,337	2,243
Amortization of intangible assets	142	146
Amortization of debt discount	17	40
Change in fair value of common stock warrant liability	(4,444)
Change in fair value of contingent consideration		(48)
Loss on abandonment and disposal of property and equipment	1,566	265
Other non-cash adjustments	(21)	3
Changes in operating assets and liabilities:
Accounts receivable	(1,648)	(881)
Inventory	(655)	(10)
Prepaid expenses and other current assets	(332)	126
Operating lease right-of-use assets	1,348	1,214
Other assets	130	25
Accounts payable and accrued expenses	(2,349)	4,095
Other current liabilities		155
Deferred revenue	(73)	(36)
Operating lease liabilities	(1,353)	(1,142)
Other long-term liabilities		571
Net cash used in operating activities	(32,170)	(40,650)
CASH FLOWS FROM INVESTING ACTIVITIES
Purchase of property and equipment	(1,225)	(2,386)
Purchase of available-for-sale securities	(14,144)	(29,002)
Proceeds from maturities of available-for-sale securities	16,945	14,636
Proceeds from sale of available-for-sale securities	16,171	1,877
Net cash provided by (used in) investing activities	17,747	(14,875)
CASH FLOWS FROM FINANCING ACTIVITIES
Net proceeds from the sale of common stock and warrants	24,276	27,948
Proceeds from stock options exercised	31	529
Proceeds from ESPP purchase	40	35
Cash paid for tax withholdings related to net share settlement	(114)	(679)
Payment of contingent consideration liability		(109)
Principal payments on financing leases	(376)	(336)
Proceeds from term note payable and financing arrangements	4,630
Principal payments on term note payable and financing arrangements	(1,096)	(263)
Net cash provided by financing activities	27,391	27,125
Net increase (decrease) in cash and cash equivalents	12,968	(28,400)
Cash and cash equivalents - beginning of period	10,218	55,673
Cash and cash equivalents - end of period	23,186	27,273
Non-cash investing and financing activities:
Unpaid liability for acquisition of property and equipment	10	249
Reclassification of stock-based compensation expense that was previously classified as a liability to paid-in capital		38
Unpaid tax liability related to net share settlement	5
Allocation of proceeds from sale of common stock and warrants to warrant liability	11,677
Property and equipment acquired through finance lease		2,341
Property and equipment acquired through financing arrangement		$ 58