Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
CASH FLOWS FROM OPERATING ACTIVITIES:
Net loss	$ (107,908)	$ (120,199)	$ (76,396)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	6,419	4,655	3,499
Stock-based compensation	22,805	19,445	14,169
Accretion on asset retirement obligation	63	43	33
Change in fair value of warrant liability	(509)	(2,496)	(9,379)
Loss on disposal of property and equipment	139	3	3
Inventory lower of cost and net realizable value adjustment	150	0	340
Amortization of debt discount and interest accrual	729	703	3,628
Loss on debt extinguishment	0	0	2,416
Product upgrade reserve	(2,294)	3,794	0
Changes in operating assets and liabilities:
Accounts receivable	5,048	20,050	(16,541)
Inventory	8,240	(5,951)	(32,214)
Deposits on purchased inventory	4,373	1,685	(1,099)
Deferred cost of revenue	(186)	1,755	3,500
Prepaid expenses and other assets	(1,356)	2,963	(2,343)
Accounts payable	(3,352)	2,759	(870)
Accrued expenses and other long-term liabilities	(292)	6,995	(9,174)
Customer deposits and deferred revenue	4,457	(15,771)	(1,766)
Net cash used in operating activities	(63,474)	(79,567)	(122,194)
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchase of property and equipment	(6,183)	(7,760)	(3,685)
Purchase of intangible and other assets	0	(57)	0
Net cash used in investing activities	(6,183)	(7,817)	(3,685)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from term loan modification	2,000	0	0
Proceeds from draw down of long-term debt, gross	0	0	56,000
Payment of debt issuance costs	(815)	(168)	(468)
Payment of long-term debt	0	0	(45,000)
Payment on debt extinguishment fee	0	0	(172)
Proceeds from employee stock purchase plan	365	0	0
Proceeds from the exercise of stock options	15	9,641	5,285
Proceeds from the exercise of warrants	0	0	3
Payments for taxes related to net share settlement of equity awards	(1,376)	(2,410)	0
Net cash (used in) provided by financing activities	(350)	146,206	236,712
NET (DECREASE) INCREASE IN CASH, CASH EQUIVALENTS AND RESTRICTED CASH	(70,007)	58,822	110,833
CASH, CASH EQUIVALENTS AND RESTRICTED CASH — BEGINNING OF PERIOD	228,187	169,365	58,532
CASH, CASH EQUIVALENTS AND RESTRICTED CASH — END OF PERIOD	158,180	228,187	169,365
SUPPLEMENTAL DISCLOSURE OF CASH FLOW INFORMATION:
Cash paid for interest	3,262	3,954	11,161
Cash paid for taxes	43	19	0
SUPPLEMENTAL NON-CASH INVESTING AND FINANCING ACTIVITIES:
Fair value of common stock warrants reclassed from liability to additional paid-in capital upon exercise	0	3,975	1,197
Right-of-use assets obtained in exchange for new operating lease liabilities	643	1,647	0
Transfer of property and equipment from inventory	1,698	4,897	2,247
Purchase of property and equipment in accounts payable and accrued expenses	59	657	157
Offering costs included in accounts payable and accrued expenses	460	730	168
Public Offering
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from offering of common stock, gross	0	149,559	172,500
Payment of offering costs related to common stock issuance	(539)	(10,416)	(10,631)
At The Market Offering Program
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from offering of common stock, gross	0	0	278
Payment of offering costs related to common stock issuance	0	0	(6)
Direct Registered Offering
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from offering of common stock, gross	0	0	59,100
Payment of offering costs related to common stock issuance	$ 0	$ 0	$ (177)