Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014
Operating Activities
Net loss	$ (19,468)	$ (18,066)
Adjustments to reconcile net loss to net cash and cash equivalents used in operating activities:
Depreciation and amortization	768	594
Amortization of debt discount	29
Amortization of debt issuance costs	25	44
Stock-based compensation	1,667	1,202
Loss on disposal of property and equipment		19
Changes in operating assets and liabilities:
Accounts receivable	125	92
Interest receivable		66
Inventory		263
Other current and long term assets	150	(13)
Restricted cash	250	125
Accounts payable	(162)	1,812
Accrued expenses	490	500
Net cash and cash equivalents used in operating activities	(16,126)	(13,362)
Investing Activities
Proceeds from sale and maturities of investments		6,191
Purchase of property and equipment	(311)	(910)
Net cash and cash equivalents (used in) provided by investing activities	(311)	5,281
Financing Activities
Payment of debt		(1,897)
Proceeds from issuance of common stock, net of issuance costs	52,533	52,506
Proceeds from exercise of stock options and warrants	250	24
Net cash and cash equivalents provided by financing activities	52,783	50,633
Net increase in cash and cash equivalents	36,346	42,552
Cash and Cash Equivalents, beginning of period	34,766	10,014
Cash and Cash Equivalents, end of period	71,112	52,566
Supplemental Disclosure for Cash Flow Information
Interest paid	$ 375	$ 337