Condensed 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	$ (4,580)us-gaap_NetIncomeLoss	$ (2,831)us-gaap_NetIncomeLoss
Reconciliation of net loss to net cash used in operating activities:
Depreciation	8	7
Amortization of premium/discount on available-for-sale securities	198	4
Accretion of discount and debt issuance cost of convertible notes payable		741
Stock-based compensation	407us-gaap_ShareBasedCompensation	17us-gaap_ShareBasedCompensation
Change in fair value of derivative liability		69
Changes in:
Prepaid expenses and other assets	103	(259)
Interest receivable	(305)	15
Accounts payable and accrued expenses	296	589
Accrued interest payable		86
Net cash used in operating activities	(3,873)	(1,562)
Investing activities
Purchases of available-for-sale investments	(58,139)
Proceeds from maturities of available-for-sale investments	2,961	2,355
Purchase of property and equipment	(5)
Net cash (used in) provided by investing activities	(55,183)	2,355
(Decrease) increase in cash and cash equivalents	(59,056)	793
Cash and cash equivalents, beginning of period	68,840	2,793
Cash and cash equivalents, end of period	9,784	3,586
Supplemental disclosure of non-cash investing and financing activities
Accretion of redeemable convertible preferred stock to redemption value		1,512
Fair value of derivative embedded within convertible notes payable		$ 1,512

Represents the accretion of redeemable convertible preferred stock to redemption.

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Represents the fair value of embedded derivative contained within convertible notes payable

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The sum of the periodic adjustments of the differences between securities' face values and purchase prices that are charged against earnings. This is called accretion if the security was purchased at a discount and amortization if it was purchased at premium. As a noncash item, this element is an adjustment to net income when calculating cash provided by or used in operations using the indirect method.

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Amount of noncash expense included in interest expense to amortize debt discount and premium associated with the related debt instruments. Excludes amortization of financing costs. Alternate captions include noncash interest expense.

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Amount of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Excludes cash and cash equivalents within disposal group and discontinued operation.

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Amount of increase (decrease) in cash and cash equivalents. Cash and cash equivalents are the amount of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Includes effect from exchange rate changes.

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Amount of cash inflow (outflow) from operating activities, excluding discontinued operations. Operating activity cash flows include transactions, adjustments, and changes in value not defined as investing or financing activities.

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The cash outflow to acquire debt and equity securities not classified as either held-to-maturity securities or trading securities which would be classified as available-for-sale securities and reported at fair value, with unrealized gains and losses excluded from earnings and reported in a separate component of shareholders' equity.

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