Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
CASH FLOWS FROM OPERATING ACTIVITIES:
Net loss	$ (57,719)	$ (53,684)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	3,171	2,957
Stock-based compensation	14,949	11,304
Accretion on asset retirement obligation	61	41
Change in fair value of warrant liabilities	4,701	(3,301)
Loss on disposal of property and equipment	0	12
Inventory lower of cost or net realizable value adjustment	0	150
Amortization of debt discount and interest accrual	471	357
Product upgrade reserve	1,000	(1,260)
Changes in operating assets and liabilities:
Accounts receivable	(3,647)	(5,272)
Inventory	4,763	6,684
Deposits on purchased inventory	(1,595)	1,814
Deferred cost of revenue	755	(4,390)
Prepaid expenses and other assets	(5,397)	(2,327)
Accounts payable	(2,508)	(8,470)
Accrued expenses and other long-term liabilities	(1,374)	(1,865)
Customer deposits and deferred revenue	2,057	12,232
Net cash used in operating activities	(40,312)	(45,018)
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchases of property and equipment	(568)	(1,295)
Net cash used in investing activities	(568)	(1,295)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from the exercise of stock options	184	15
Proceeds from the exercise of warrants	2	0
Proceeds from employee stock purchase plan	264	156
Payments for taxes related to net share settlement of equity awards	(2,759)	(132)
Net cash provided by (used in) financing activities	51,085	(500)
NET INCREASE (DECREASE) IN CASH DURING THE PERIOD	10,205	(46,813)
CASH, CASH EQUIVALENTS AND RESTRICTED CASH — BEGINNING OF PERIOD	158,180	228,187
CASH, CASH EQUIVALENTS AND RESTRICTED CASH — END OF PERIOD	168,385	181,374
SUPPLEMENTAL DISCLOSURE OF CASH FLOW INFORMATION:
Cash paid for interest	1,648	2,140
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	0	0
Transfer of property and equipment from inventory and deferred cost of revenue	0	1,583
Purchases of property and equipment in accounts payable and accrued liabilities	351	65
Public Offering
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)