Consolidated Statements of Cash Flows (Unaudited) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Operating Activities
Net loss	$ (10,120)	$ (7,479)
Adjustments to reconcile net loss to net cash and cash equivalents used in operating activities:
Depreciation and amortization	390	286
Amortization of debt discount	15
Amortization of debt issuance costs	12	22
Stock-based compensation	899	405
Changes in operating assets and liabilities:
Accounts receivable	80	136
Interest receivable		(5)
Inventory		50
Other current and long term assets	143	(178)
Restricted cash		125
Accounts payable	510	54
Accrued expenses	(143)	125
Net cash and cash equivalents used in operating activities	(8,214)	(6,459)
Investing Activities
Proceeds from sale and maturities of investments		1,722
Purchase of property and equipment	(155)	(187)
Net cash and cash equivalents used in investing activities	(155)	(1,535)
Financing Activities
Payment of debt		(938)
Proceeds from issuance of common stock, net of issuance costs	1,783
Proceeds from exercise of stock options	196	8
Net cash and cash equivalents provided by (used in) financing activities	1,979	(930)
Net decrease in cash and cash equivalents	(6,390)	(5,854)
Cash and Cash Equivalents, beginning of period	34,766	10,014
Cash and Cash Equivalents, end of period	28,376	4,160
Supplemental Disclosure for Cash Flow Information
Interest paid	$ 187	$ 179