Condensed Consolidated Statements of Cash Flows (Statement) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
CASH FLOWS FROM OPERATING ACTIVITIES:
Net loss	$ (82,980)	$ (81,809)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	4,644	4,372
Stock-based compensation	19,583	17,063
Accretion on asset retirement obligation	83	62
Change in fair value of warrant liabilities	5,577	(1,281)
Loss on disposal of property and equipment	0	121
Inventory lower of cost or net realizable value adjustment	417	150
Amortization of debt discount and interest accrual	694	527
Product upgrade reserve	1,000	(1,260)
Changes in operating assets and liabilities:
Accounts receivable	(10,209)	(9,731)
Inventory	8,349	8,425
Deposits on purchased inventory	(2,642)	2,203
Deferred cost of revenue	616	(6,937)
Prepaid expenses and other assets	(5,126)	(1,268)
Accounts payable	(1,934)	(6,031)
Accrued expenses and other long-term liabilities	(278)	(1,416)
Customer deposits and deferred revenue	5,817	17,130
Net cash used in operating activities	(56,389)	(59,680)
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchases of property and equipment	(839)	(2,201)
Net cash used in investing activities	(839)	(2,201)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from common stock public offering, gross	57,385	0
Payment of offering costs related to common stock public offering	(3,991)	(539)
Proceeds from the exercise of stock options	611	15
Proceeds from the exercise of warrants	2	0
Proceeds from employee stock purchase plan	264	313
Payments for taxes related to net share settlement of equity awards	3,863	754
Net cash provided by (used in) financing activities	50,408	(965)
NET DECREASE CASH DURING THE PERIOD	(6,820)	(62,846)
CASH, CASH EQUIVALENTS AND RESTRICTED CASH — BEGINNING OF PERIOD	158,180	228,187
CASH, CASH EQUIVALENTS AND RESTRICTED CASH — END OF PERIOD	151,360	165,341
SUPPLEMENTAL DISCLOSURE OF CASH FLOW INFORMATION:
Cash paid for interest	2,485	2,695
Cash paid for income taxes	0	28
SUPPLEMENTAL NON-CASH INVESTING AND FINANCING ACTIVITIES:
Fair value of common stock warrants reclassified from liability to additional paid-in capital upon exercise	351	0
Right-of-use assets obtained in exchange for new operating lease liabilities	1,693	0
Transfer of property and equipment from inventory and deferred cost of revenue	0	1,698
Purchases of property and equipment in accounts payable and accrued liabilities	$ 134	$ 381