Condensed Consolidated Balance Sheets (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Current assets:
Cash and cash equivalents	$ 43,188	$ 14,776
Short-term investments	16,515	16,615
Prepaid expenses and other current assets	481	574
Total current assets	60,184	31,965
Property and equipment, net	895	756
Other assets	88	93
Total assets	61,167	32,814
Current liabilities:
Accounts payable	948	875
Accrued expenses	1,146	1,211
Total current liabilities	2,094	2,086
Other non-current liabilities	11	7
Total liabilities	2,105	2,093
Commitments and contingencies
Stockholder's equity:
Preferred stock, $0.001 par value; 5,000,000 shares authorized; no shares issued and outstanding
Common stock, $0.001 par value per share; 23,000,000 shares authorized; 18,191,159 and 14,268,068 shares issued at March 31, 2013 and December 31, 2012, respectively; 16,710,525 and 12,622,919 shares outstanding at March 31, 2013 and December 31, 2012, respectively	18	14
Additional paid-in capital	80,334	46,847
Accumulated other comprehensive income (loss)	1	(6)
Deficit accumulated during the development stage	(21,291)	(16,134)
Total stockholders' equity	59,062	30,721
Total liabilities and stockholders' equity	$ 61,167	$ 32,814