CONDENSED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014
Cash flows from operating activities
Net loss	$ (33,888)	$ (23,829)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	961	1,132
Amortization of debt issuance costs and debt discount	152	167
Stock-based compensation	3,691	509
Remeasurement of warrant and embedded derivatives	(835)	(67)
Write off of embedded derivatives	1,066
Noncash interest expense and other charges	1,735	2,999
Loss on extinguishment of convertible notes	86	892
Provision for excess and obsolete inventories	(57)	(47)
Changes in operating assets and liabilities:
Accounts receivable	(93)	(271)
Inventories	332	1,298
Prepaid expenses and other current assets	(510)	69
Other assets	(6)	(326)
Accounts payable	(552)	104
Accrued compensation	1,185	279
Accrued expenses and other current liabilities	(994)	1,511
Other long-term liabilities and accrued interest	(1,637)	(168)
Net cash used in operating activities	(29,364)	(15,748)
Cash flows from investing activities:
Purchase of property and equipment	(288)	(37)
Restricted cash	255
Net cash used in investing activities	(33)	(37)
Cash flows from financing activities:
Principal paydown of capital lease obligations	(15)	(14)
Payments on borrowing	(27,625)
Proceeds from convertible notes, net of issuance costs		4,700
Proceeds from borrowing, net of issuance costs	29,124	11,074
Proceeds from the issuance of convertible preferred stock, net of issuance costs	6,176
Proceeds from the issuance of common stock related to CRG loan, net of issuance costs	4,794
Proceeds from initial public offering, net of issuance costs	58,746
Proceeds from the exercise of common stock warrants	308
Proceeds from the issuance of common stock	354	17
Net cash provided by financing activities	71,862	15,777
Net change in cash and cash equivalents	42,465	(8)
Cash and cash equivalents, beginning of period	12,316	12,221
Cash and cash equivalents, end of period	54,781	12,213
Supplemental disclosure of cash flow information
Cash paid for interest	5,030	1,743
Noncash investing and financing activities:
Conversion of convertible notes and accrued interest into Series E convertible preferred stock	137,632
Modification of convertible preferred stock	2,384
Reclass of warrant liability to additional paid-in capital		34
Vesting of common stock subject to repurchase	17	7
Issuance of common stock warrants	804	129
Transfer between inventory and property and equipment	$ 512	848
Conversion of convertible notes and accrued interest into Series E convertible preferred stock		$ 7,794