Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015
Operating activities
Net loss	$ (27,472)	$ (21,614)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	1,068	600
Stock-based compensation expense	2,527	1,577
Noncash interest expense	308	180
Deferred rent	(123)	(67)
Changes in operating assets and liabilities:
Accounts receivable	81	(188)
Prepaid expenses and other assets	276	447
Inventory	(752)	(453)
Accounts payable	(49)	827
Accrued expenses and other liabilities	228	(396)
Deferred revenue	(879)	1,695
Net cash used in operating activities	(24,787)	(17,392)
Investing activities
Purchases and manufacture of property and equipment	(3,173)	(4,184)
Decrease in restricted cash		80
Net cash used in investing activities	(3,173)	(4,104)
Financing activities
Payment of offering costs for issuance of common stock in public offering	(385)
Proceeds from issuance of common stock and stock options exercises, net	700	1,088
Proceeds from notes payable, net of issuance costs	4,593
Repayments of notes payable	(392)	(152)
Net cash provided by financing activities	4,516	936
Net decrease in cash and cash equivalents	(23,444)	(20,560)
Cash and cash equivalents at beginning of period	73,662	73,849
Cash and cash equivalents at end of period	50,218	53,289
Supplemental disclosures of cash flow information
Cash paid for interest	1,146	716
Supplemental disclosures of noncash investing and financing activities
Accrued property and equipment	$ 184	$ 1,595