Condensed Consolidated Statements of Cash Flows - USD ($)	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
CASH FLOWS FROM OPERATING ACTIVITIES:
Net loss	$ (19,574,000)	$ (27,270,000)
Adjustments to reconcile net loss to net cash used in operating activities:
Interest expense on promissory notes	2,536,000	2,297,000
Stock-based compensation expense	3,313,000	3,672,000
Asset impairment	1,889,000
Depreciation, amortization and accretion	1,105,000	739,000
Amortization of right-of-use assets	576,000	618,000
Write-off of inventory	496,000	0
Loss (gain) on foreign currency translation	71,000	(688,000)
Other, net	19,000
Changes in operating assets and liabilities:
Accounts receivable, net	147,000	(957,000)
Inventory	(164,000)	(366,000)
Prepaid expenses and other current assets	1,352,000	(150,000)
Other assets	82,000	(356,000)
Accounts payable	1,032,000	2,154,000
Accrued expenses and other current liabilities	(1,343,000)	460,000
Deferred revenue	(3,803,000)	(6,795,000)
Operating lease liabilities	(1,401,000)	(699,000)
Recognized loss on purchase commitments	(1,236,000)	(3,984,000)
Net cash used in operating activities	(14,903,000)	(31,325,000)
CASH FLOWS FROM INVESTING ACTIVITIES:
Proceeds from sale of treasury bills	20,000,000
Purchase of property and equipment	(300,000)	(1,493,000)
Purchase of treasury bills		(24,909,000)
Net cash provided by (used in) investing activities	19,700,000	(26,402,000)
CASH FLOWS FROM FINANCING ACTIVITIES:
Issuance of common stock from the exercise of warrants	11,600,000
Proceeds from Paycheck Protection Program loan	4,873,000
Payment of employment taxes related to vested restricted stock units and exercise of stock options	(201,000)	18,000
Proceeds from market price stock purchase plan	14,000
Principal payments on facility financing obligation		(2,500,000)
Net cash provided by (used in) financing activities	28,519,000	(673,000)
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS AND RESTRICTED CASH	33,316,000	(58,400,000)
CASH AND CASH EQUIVALENTS AND RESTRICTED CASH, BEGINNING OF PERIOD	30,222,000	71,684,000
CASH AND CASH EQUIVALENTS AND RESTRICTED CASH, END OF PERIOD	63,538,000	13,284,000
SUPPLEMENTAL CASH FLOWS DISCLOSURES:
Interest paid in cash, net of amounts capitalized	1,820,000
NON-CASH INVESTING AND FINANCING ACTIVITIES:
Payment of principal on senior convertible notes through common stock issuance	2,630,000
Receivable from at the market offering	470,000
Common stock issuance to settle employee stock purchase plan liability	318,000	317,000
Payment of interest on senior convertible notes through common stock issuance	144,000	538,000
Addition of right-of-use assets upon adoption of new lease guidance		5,192,000
Non-cash construction in progress and property and equipment		790,000
At The Market Issuance
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from at the market offering	12,564,000	1,850,000
Issuance costs associated with at the market offering	$ (331,000)	$ (41,000)