CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (USD $) In Thousands, unless otherwise specified	9 Months Ended
Sep. 30, 2014	Sep. 30, 2013
Cash flows from operating activities:
Net loss	$ (23,731)	$ (18,338)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	313	565
Stock-based compensation	3,596	2,800
Amortization of intangible assets	750	750
Gain on sale of assets		(630)
Other non-cash items		13
Changes in assets and liabilities:
Accounts receivable	(27)	233
Prepaid expenses and other assets	357	(173)
Inventory	(190)	(195)
Deferred revenue	(94)	(276)
Accounts payable	(118)	(198)
Accrued expenses and other liabilities	433	(2,268)
Net cash used in operating activities	(18,711)	(17,717)
Cash flows from investing activities:
Purchases of property and equipment	(289)	(120)
Net proceeds from sale of assets		630
Proceeds from sales and maturities of marketable securities	32,985	40,967
Purchases of marketable securities	(15,859)	(53,885)
Net cash provided by investing activities	16,837	(12,408)
Cash flows from financing activities:
Net proceeds from issuance of common stock	2,195	2,024
Proceeds from the sale of common stock, net of issuance costs		27,746
Net cash provided by financing activities	2,195	29,770
Net increase (decrease) in cash and cash equivalents	321	(355)
Cash and cash equivalents at beginning of period	4,364	2,529
Cash and cash equivalents at end of period	$ 4,685	$ 2,174

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The aggregate expense charged against earnings to allocate the cost of intangible assets (nonphysical assets not used in production) in a systematic and rational manner to the periods expected to benefit from such assets. As a noncash expense, this element is added back to net income when calculating cash provided by or used in operations using the indirect method.