Consolidated Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Operating Activities
Net loss	$ (37,652)	$ (28,358)
Adjustments to reconcile net loss to net cash and cash equivalents used in operating activities:
Depreciation and amortization	1,310	1,483
Amortization of debt discount	14
Amortization of debt issuance costs	69	103
Remeasurement of fair value of preferred stock warrant liability		1,800
Accretion/amortization of bond discount/premium		52
Stock-based compensation	1,840	941
Loss on disposal of property and equipment	86	31
Impairment loss on property and equipment		450
Changes in operating assets and liabilities:
Accounts receivable	55	402
Interest receivable	67	(52)
Inventory	701	731
Other current and long term assets	(170)	(328)
Restricted cash	125
Accounts payable	(36)	641
Accrued expenses	363	868
Net cash and cash equivalents used in operating activities	(33,228)	(21,236)
Investing Activities
Purchase of investments		(6,240)
Proceeds from sale and maturities of investments	6,191	904
Cash received in acquisition of a business, net of cash paid		246
Purchase of property and equipment	(2,174)	(1,377)
Proceeds from sale of property and equipment	25
Net cash and cash equivalents provided by (used in) investing activities	4,042	(6,467)
Financing Activities
Proceeds from issuance of debt, net of debt discount	4,321	1,998
Payment of debt	(2,877)	(1,519)
Proceeds from issuance of common stock, net of issuance costs	52,433
Proceeds from issuance of preferred stock, net of issuance costs		28,199
Debt issuance costs	(30)
Proceeds from exercise of stock options and restricted stock units	75
Proceeds from exercise of warrants	16	143
Net cash and cash equivalents provided by financing activities	53,938	28,821
Net increase in cash and cash equivalents	24,752	1,118
Cash and Cash Equivalents, beginning of year	10,014	8,896
Cash and Cash Equivalents, end of year	34,766	10,014
Supplemental Disclosure for Cash Flow Information
Interest paid	904	824
Supplemental Schedule of Noncash Investing and Financing Activities
Issuance of common stock warrants	54
Conversion of bridge notes to preferred stock		1,998
Conversion of preferred stock warrants to common stock warrants		1,909
Conversion of preferred stock to common stock		$ 30,197