CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Cash flows from operating activities:
Net loss	$ (8,087)	$ (4,997)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	108	211
Stock-based compensation	1,491	888
Amortization of intangible assets	250	250
Gain on sale of assets		(630)
Other non-cash items		5
Changes in assets and liabilities:
Accounts receivable	(205)	219
Prepaid expenses and other assets	158	(88)
Inventory	(80)	(10)
Deferred revenue	(15)	(145)
Accounts payable	99	1,202
Accrued expenses and other liabilities	(56)	(1,892)
Net cash used in operating activities	(6,337)	(4,987)
Cash flows from investing activities:
Purchases of property and equipment	(84)	(57)
Net proceeds from sale of assets		630
Proceeds from sales and maturities of marketable securities	13,531	15,589
Purchases of marketable securities	(10,985)	(9,433)
Net cash provided by investing activities	2,462	6,729
Cash flows from financing activities:
Proceeds from issuance of common stock	1,624	1,008
Net cash provided by financing activities	1,624	1,008
Net (decrease) increase in cash and cash equivalents	(2,251)	2,750
Cash and cash equivalents at beginning of period	4,364	2,529
Cash and cash equivalents at end of period	$ 2,113	$ 5,279