Condensed Consolidated Balance Sheets (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Current assets:
Cash and cash equivalents	$ 19,082	$ 9,087
Prepaid expenses and other current assets	304	706
Total current assets	19,386	9,793
Property and equipment, net	789	1,161
Other assets	2,743
Restricted cash	122	122
Total assets	23,040	11,076
Current liabilities:
Accounts payable and accrued expenses	3,725	2,268
Current portion of deferred revenue		63
Current portion of deferred rent	45	251
Convertible notes, net of discount	3,481
Repurchase liability for unvested equity awards	106	143
Preferred stock warrant liability	163	184
Long-term debt, current portion	1,971	1,941
Total current liabilities	9,491	4,850
Deferred rent	153	132
Accrued expenses	137	110
Exchangeable share liability	2,885	551
Long-term debt, less current portion	250	1,732
Long-term convertible notes	20,000
Commitments and contingencies
Convertible preferred stock, $0.001 par value; authorized shares - 68,360,186 at September 30, 2013 and 62,200,000 at December 31, 2012; issued and outstanding shares - 44,967,690 at September 30, 2013 and December 31, 2012; liquidation preference of $58,518 at September 30, 2013 and December 31, 2012	56,526	56,526
Stockholders' deficit:
Common stock, $0.001 par value; authorized shares - 110,000,000 at September 30, 2013 and 100,000,000 at December 31, 2012; issued and outstanding shares - 1,377,659 at September 30, 2013 and 1,334,115 at December 31, 2012	1	1
Additional paid-in capital	14,367	12,789
Deficit accumulated during the development stage	(80,770)	(65,615)
Total stockholders' deficit	(66,402)	(52,825)
Total liabilities, convertible preferred stock and stockholders' deficit	$ 23,040	$ 11,076