Consolidated Statements of Cash Flows - USD ($)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
CASH FLOWS FROM OPERATING ACTIVITIES:
Net loss	$ (110,048,000)	$ (107,908,000)	$ (120,199,000)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	5,984,000	6,419,000	4,655,000
Stock-based compensation	23,871,000	22,805,000	19,445,000
Accretion on asset retirement obligation	105,000	63,000	43,000
Change in fair value of warrant liability	2,284,000	(509,000)	(2,496,000)
Loss on disposal of property and equipment	0	139,000	3,000
Inventory lower of cost and net realizable value adjustment	883,000	150,000	0
Amortization of debt discount and interest accrual	919,000	729,000	703,000
Product upgrade reserve	1,000,000	(2,294,000)	3,794,000
Changes in operating assets and liabilities:
Accounts receivable	(9,890,000)	5,048,000	20,050,000
Inventory	15,565,000	8,240,000	(5,951,000)
Deposits on purchased inventory	(2,694,000)	4,373,000	1,685,000
Deferred cost of revenue	(1,388,000)	(186,000)	1,755,000
Prepaid expenses and other assets	(5,550,000)	(1,356,000)	2,963,000
Accounts payable	(746,000)	(3,352,000)	2,759,000
Accrued expenses and other long-term liabilities	6,807,000	(292,000)	6,995,000
Customer deposits and deferred revenue	10,807,000	4,457,000	(15,771,000)
Net cash used in operating activities	(62,091,000)	(63,474,000)	(79,567,000)
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchase of property and equipment	(1,559,000)	(6,183,000)	(7,760,000)
Purchase of intangible and other assets	0	0	(57,000)
Net cash used in investing activities	(1,559,000)	(6,183,000)	(7,817,000)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from term loan modification	0	2,000,000	0
Payment of debt issuance costs	0	(815,000)	(168,000)
Proceeds from common stock public offerings, gross	137,884,000	0	149,559,000
Payment of offering costs related to common stock public offerings	(9,334,000)	(539,000)	(10,416,000)
Proceeds from employee stock purchase plan	550,000	365,000	0
Proceeds from the exercise of stock options	775,000	15,000	9,641,000
Proceeds from the exercise of warrants	3,000	0	0
Payments for taxes related to net share settlement of equity awards	(4,600,000)	(1,376,000)	(2,410,000)
Net cash provided by (used in) financing activities	125,278,000	(350,000)	146,206,000
NET (DECREASE) INCREASE IN CASH, CASH EQUIVALENTS AND RESTRICTED CASH	61,628,000	(70,007,000)	58,822,000
CASH, CASH EQUIVALENTS AND RESTRICTED CASH — BEGINNING OF PERIOD	158,180,000	228,187,000	169,365,000
CASH, CASH EQUIVALENTS AND RESTRICTED CASH — END OF PERIOD	219,808,000	158,180,000	228,187,000
SUPPLEMENTAL DISCLOSURE OF CASH FLOW INFORMATION:
Cash paid for interest	3,323,000	3,262,000	3,954,000
Cash paid for taxes	0	43,000	19,000
SUPPLEMENTAL NON-CASH INVESTING AND FINANCING ACTIVITIES:
Fair value of common stock warrants reclassed from liability to additional paid-in capital upon exercise	352,000	0	3,975,000
Right-of-use assets obtained in exchange for new operating lease liabilities	1,693,000	643,000	1,647,000
Transfer of property and equipment from inventory	576,000	1,698,000	4,897,000
Purchase of property and equipment in accounts payable and accrued expenses	82,000	59,000	657,000
Offering costs included in accounts payable and accrued expenses	$ 25,000	$ 460,000	$ 730,000