Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
CASH FLOWS FROM OPERATING ACTIVITIES:
Net loss	$ (120,199)	$ (76,396)	$ (72,176)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	4,655	3,499	2,197
Stock-based compensation	19,445	14,169	5,319
Accretion on asset retirement obligation	43	33	40
Change in fair value of warrant liability	(2,496)	(9,379)	16,598
Loss on disposal of property and equipment	3	3	9
Inventory lower of cost and net realizable value adjustment	0	340	911
Amortization of debt discount and interest accrual	703	3,628	3,321
Loss on debt extinguishment	0	2,416	0
Product upgrade reserve	3,794	0	0
Changes in operating assets and liabilities:
Accounts receivable	20,050	(16,541)	(16,126)
Inventory	(5,951)	(32,214)	(12,329)
Deposits on purchased inventory	1,685	(1,099)	(4,521)
Deferred cost of revenue	1,755	3,500	(9,787)
Prepaid expenses and other assets	2,963	(2,343)	(2,044)
Accounts payable	2,759	(870)	6,309
Accrued expenses and other long-term liabilities	6,995	(9,174)	850
Customer deposits and deferred revenue	(15,771)	(1,766)	11,376
Net cash used in operating activities	(79,567)	(122,194)	(70,053)
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchase of property and equipment	(7,760)	(3,685)	(2,163)
Purchase of intangible and other assets	(57)	0	0
Net cash used in investing activities	(7,817)	(3,685)	(2,163)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from draw down of long-term debt, gross	0	56,000	0
Payment of debt issuance costs	(168)	(468)	0
Payment of long-term debt	0	(45,000)	0
Payment on debt extinguishment fee	0	(172)	0
Proceeds from common stock private placement, gross	0	0	26,100
Proceeds from the exercise of stock options	9,641	5,285	665
Proceeds from the exercise of warrants	0	3	103
Payments for taxes related to net share settlement of equity awards	(2,410)	0	0
Net cash provided by financing activities	146,206	236,712	115,407
NET INCREASE IN CASH, CASH EQUIVALENTS AND RESTRICTED CASH	58,822	110,833	43,191
CASH, CASH EQUIVALENTS AND RESTRICTED CASH — BEGINNING OF PERIOD	169,365	58,532	15,341
CASH, CASH EQUIVALENTS AND RESTRICTED CASH — END OF PERIOD	228,187	169,365	58,532
SUPPLEMENTAL DISCLOSURE OF CASH FLOW INFORMATION:
Cash paid for interest	3,954	11,161	3,925
Cash paid for taxes	19	0	1
SUPPLEMENTAL NON-CASH INVESTING AND FINANCING ACTIVITIES:
Fair value of common stock warrants reclassed from liability to additional paid-in capital upon exercise	3,975	1,197	274
Right-of-use assets obtained in exchange for new operating lease liabilities	1,647	0	0
Transfer of property and equipment from inventory	4,897	2,247	125
Purchase of property and equipment in accounts payable and accrued expenses	657	157	96
Offering costs included in accounts payable and accrued expenses	730	168	0
Public Offering
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from offering of common stock, gross	149,559	172,500	0
Payment of offering costs related to common stock issuance	(10,416)	(10,631)	0
Private Placement
CASH FLOWS FROM FINANCING ACTIVITIES:
Payment of offering costs related to common stock issuance	0	0	(300)
At The Market Offering Program
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from offering of common stock, gross	0	278	40,126
Payment of offering costs related to common stock issuance	0	(6)	(1,147)
Direct Registered Offering
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from offering of common stock, gross	0	59,100	49,941
Payment of offering costs related to common stock issuance	$ 0	$ (177)	$ (81)