Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Operating activities:
Net income (loss)	$ (1,673)	$ 900	$ 297
Adjustment to reconcile net income (loss) to net cash provided by (used in) operating activities:
Depreciation and amortization	2,869	1,972	1,366
Amortization and write-off of debt issuance costs	239	152	182
Amortization of premium on short-term investments	31
Revaluation of warrant liability	(559)	(703)	398
Stock-based compensation	2,765	1,178	1,175
Changes in operating assets and liabilities:
Accounts receivable	(4,515)	(3,327)	(3,611)
Inventory	(15,897)	(2,783)	(799)
Prepaid expenses and other assets	(1,759)	(360)	(159)
Deferred revenue	17	(466)	(896)
Deferred rent	86	4,601	(165)
Accounts payable	3,883	754	1,402
Accrued compensation and benefits	3,462	1,356	(817)
Accrued liabilities	1,554	182	795
Net cash provided by (used in) operating activities	(9,497)	3,456	(832)
Investing activities:
Purchases of investments	(67,103)
Purchases of property and equipment	(3,530)	(7,450)	(1,017)
Restricted cash			200
Net cash used in investing activities	(70,633)	(7,450)	(817)
Financing activities:
Proceeds from public offerings, net of offering costs	108,096
Payments on capital lease financing obligations	(1,229)	(824)	(625)
Payments on term loans	(65,320)	(6,115)	(2,667)
Proceeds from term loans	61,436	13,899
Proceeds from exercise of stock options	600	538	702
Proceeds from exercise of warrants	62
Payments of deferred offering costs		(322)
Net cash provided by (used in) financing activities	103,645	7,176	(2,590)
Net increase (decrease) in cash and cash equivalents	23,515	3,182	(4,239)
Cash and cash equivalents:
Beginning of period	10,121	6,939	11,178
End of period	33,636	10,121	6,939
Supplemental disclosure of cash flow information:
Cash paid for interest	1,503	973	718
Cash paid for income taxes	46	41	21
Supplemental disclosure of non-cash financing and investing activities:
Accretion on preferred stock	6,258	11,301	11,301
Vesting of early exercised stock options	167	119	54
Additions to property and equipment through capital lease	341	2,907	819
Accrued not yet paid offering costs	626	315
Purchases of property and equipment not yet paid	1,538	347	$ 381
Write-off of fully depreciated property and equipment	1,571	$ 1,913
Conversion of convertible preferred stock to common stock	106,084
Conversion of convertible preferred stock warrants to common stock warrants	$ 505