Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
CASH FLOWS FROM OPERATING ACTIVITIES:
Net loss	$ (76,396)	$ (72,176)	$ (50,636)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	3,499	2,197	1,708
Stock-based compensation	14,169	5,319	2,907
Accretion on asset retirement obligation	33	40	36
Change in fair value of warrant liability	(9,379)	16,598	(3)
Loss on disposal of property and equipment	3	9	358
Inventory lower of cost and net realizable value adjustment	340	911	1,939
Amortization of debt discount and interest accrual	3,628	3,321	2,629
Loss on debt extinguishment	2,416	0	0
Changes in operating assets and liabilities:
Accounts receivable	(16,541)	(16,126)	(3,370)
Inventory	(32,214)	(12,329)	(2,065)
Deposits on purchased inventory	(1,099)	(4,521)	1,414
Deferred cost of revenue	3,500	(9,787)	4,873
Prepaid expenses and other assets	(2,343)	(2,044)	(1,633)
Accounts payable	(870)	6,309	381
Accrued expenses and other long-term liabilities	(9,174)	850	2,197
Customer deposits and deferred revenue	(1,766)	11,376	11,109
Net cash used in operating activities	(122,194)	(70,053)	(28,156)
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchase of property and equipment	(3,685)	(2,163)	(7,031)
Purchase of intangible and other assets	0	0	(12)
Net cash used in investing activities	(3,685)	(2,163)	(7,043)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from draw down of long-term debt, gross	56,000	0	15,000
Payment of debt issuance cost	(468)	0	(18)
Payment of long-term debt	(45,000)	0	0
Payment on debt extinguishment fee	(172)	0	0
Proceeds from common stock private placement, gross	0	26,100	13,750
Proceeds from the exercise of stock options	5,285	665	539
Proceeds from the exercise of warrants	3	103	0
Net cash provided by financing activities	236,712	115,407	28,930
NET INCREASE (DECREASE) IN CASH, CASH EQUIVALENTS AND RESTRICTED CASH	110,833	43,191	(6,269)
CASH, CASH EQUIVALENTS AND RESTRICTED CASH — BEGINNING OF PERIOD	58,532	15,341	21,610
CASH, CASH EQUIVALENTS AND RESTRICTED CASH — END OF PERIOD	169,365	58,532	15,341
SUPPLEMENTAL DISCLOSURE OF CASH FLOW INFORMATION:
Cash paid for interest	11,161	3,925	3,310
Cash paid for taxes	0	1	0
SUPPLEMENTAL NON-CASH INVESTING AND FINANCING ACTIVITIES:
Fair value of common stock warrants reclassed from liability to additional paid-in capital upon exercise	1,197	274	0
Transfer of property and equipment from inventory	2,247	125	117
Purchase of property and equipment in accounts payable and accrued expenses	157	96	193
Offering costs included in accounts payable and accrued expenses	168	0	189
Public Offering
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from offering of common stock, gross	172,500	0	0
Payment of offering costs related to common stock issuance	(10,631)	0	0
Private Placement
CASH FLOWS FROM FINANCING ACTIVITIES:
Payment of offering costs related to common stock issuance	0	(300)	(341)
At The Market Offering Program
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from offering of common stock, gross	278	40,126	0
Payment of offering costs related to common stock issuance	(6)	(1,147)	0
Direct Registered Offering
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from offering of common stock, gross	59,100	49,941	0
Payment of offering costs related to common stock issuance	$ (177)	$ (81)	$ 0