Consolidated Statements of Operations and Comprehensive Loss (USD $) In Thousands, except Per Share data, unless otherwise specified	9 Months Ended	12 Months Ended	21 Months Ended
	Dec. 31, 2011	Dec. 31, 2012	Dec. 31, 2012
Operating expenses:
Research and development	$ 1,170	$ 6,323	$ 7,493
General and administrative	1,454	7,206	8,660
Total operating expenses	2,624	13,529	16,153
Loss from operations	(2,624)	(13,529)	(16,153)
Interest income		19	19
Net loss	(2,624)	(13,510)	(16,134)
Accretion of convertible preferred stock to redemption value	(101)		(101)
Net loss applicable to common stockholders	(2,725)	(13,510)	(16,235)
Net loss per share applicable to common stockholders-basic and diluted (in dollars per share)	$ (3.00)	$ (2.33)	$ (4.35)
Weighted average number of common shares used in net loss per share applicable to common stockholders-basic and diluted (in shares)	909	5,810	3,734
Net loss	(2,624)	(13,510)	(16,134)
Other comprehensive loss:
Unrealized losses on available-for-sale securities		(6)	(6)
Comprehensive loss	$ (2,624)	$ (13,516)	$ (16,140)