Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014
Cash flow from operating activities:
Net loss	$ (23,505)	$ (22,099)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	561	371
Change in provision for excess inventory	(174)	1,465
Stock-based compensation and 401(k) Plan employer match	1,228	1,975
Fair value adjustment of common stock warrants	(438)	(1,826)
Amortization of discount on long-term debt	1,149	909
Loss from sale and disposal of long-lived assets	84	0
Changes in:
Inventory	201	(2,196)
Accounts receivable	0	26
Prepaid expenses and other current assets	250	334
Accounts payable	1,964	74
Accrued expenses	497	1,166
Deferred revenue	(43)	(34)
Other liabilities	(110)	(423)
Net cash used in operating activities	(18,336)	(20,258)
Cash flows from investing activities:
Purchase of property and equipment	(503)	(883)
Proceeds from sale of property and equipment	260	0
Net cash used in investing activities	(243)	(883)
Cash flows from financing activities:
Proceeds from exercise of common stock options	0	31
Proceeds from exercise of common stock warrants	0	423
Repayment of equipment loans	(41)	(39)
Net cash (used in) / provided by financing activities	(41)	415
Net decrease in cash and cash equivalents	(18,620)	(20,726)
Cash and cash equivalents - beginning of period	44,711	86,283
Cash and cash equivalents - end of period	26,091	65,557
Supplementary disclosure of cash flows information:
Interest paid	$ 1,303	$ 1,305