Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
CASH FLOWS FROM OPERATING ACTIVITIES:
Net loss	$ (50,636)	$ (44,995)	$ (33,800)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	1,708	1,256	1,020
Stock-based compensation	2,907	1,066	318
Change in fair value of warrant liability	(3)	(45)	(20)
Inventory lower of cost and market adjustment	1,939	2,578	598
Write-off of deferred offering cost		2,920
Amortization of debt discount and interest accrual	2,629	1,129	446
Loss on disposal of property and equipment	358	12	8
Accretion on asset retirement obligation	36	8
Changes in operating assets and liabilities:
Accounts receivable	(3,370)	74	(650)
Inventory	(2,065)	(2,413)	(3,279)
Deposits on purchased inventory	1,414	(1,138)	(479)
Deferred cost of revenue	4,873	(4,070)	(4,712)
Prepaid expenses and other current assets	(1,694)	(703)	13
Other assets	61	(30)	28
Accounts payable	381	(2,053)	4,033
Notes payable		(240)
Accrued expenses and other long-term liabilities	2,197	1,532	(1,048)
Customer deposits and deferred revenue	11,109	5,263	10,055
Net cash used in operating activities	(28,156)	(39,849)	(27,469)
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchase of property and equipment	(7,031)	(4,151)	(2,003)
Purchase of intangible and other assets	(12)	(104)
Change in restricted cash balance	(200)	110	(600)
Net cash used in investing activities	(7,243)	(4,145)	(2,603)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from issuance of convertible notes, net			9,941
Repurchase of Series A convertible preferred stock			(37)
Proceeds from issuance of convertible preferred stock, net		15,729	4,969
Proceeds from draw down of long-term debt	15,000	30,000
Payment of debt issuance cost	(18)	(1,132)
Payments of long-term debt		(15,000)
Proceeds from common stock private placement, gross	13,750	29,447
Payment of offering costs related to common stock private placement	(341)	(2,808)
Payments of costs related to the initial public offering		(2,728)	(222)
Proceeds from the exercise of stock options	539	24	21
Net cash provided by financing activities	28,930	53,532	14,672
NET (DECREASE) INCREASE IN CASH	(6,469)	9,538	(15,400)
CASH — Beginning of period	20,667	11,129	26,529
CASH — End of period	14,198	20,667	11,129
SUPPLEMENTAL DISCLOSURE OF CASH FLOW INFORMATION:
Cash paid for interest	3,310	2,332	1,504
Cash paid for taxes		1
SUPPLEMENTAL NON-CASH INVESTING AND FINANCING ACTIVITIES:
Transfer of property and equipment from inventory	117
Offering costs related to private placements and initial public offering included in accounts payable and accrued expenses	189		1,197
Conversion of convertible preferred stock warrants into common stock warrants in connection with the Merger		160,839
Conversion of convertible notes into new Series C convertible preferred stock			10,129
Purchase of fixed assets in accounts payable and accrued expenses	$ 193	1,136	$ 62
Fair value of common stock warrants issued to placement agents as payment for service		316
Asset retirement obligation		258
Conversion of convertible preferred stock warrants into common stock warrants		$ 93