Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2014

Summary of Significant Accounting Policies

Schedule of fair value of financial assets and liabilities measured at fair value and classification by level of input

	Fair Value Measurements as of
	December 31, 2014
(in thousands)	Level 1		Level 2		Level 3		Total
Investments:
Money market funds	$	9,663	$	—	$	—	$	9,663
Federal agency securities		—		13,770		—		13,770
Commercial paper		—		1,500		—		1,500
Corporate debt securities		—		14,520		—		14,520
Total assets measured at fair value	$	9,663	$	29,790		—	$	39,453
Financing derivative		—		—		89		89
Total liabilities measured at fair value	$	—	$	—	$	89	$	89

	Fair Value Measurements as of
	December 31, 2013
(in thousands)	Level 1		Level 2		Level 3		Total
Investments:
Money market funds	$	53,511	$	—	$	—	$	53,511
Federal agency securities		—		12,301		—		12,301
Commercial paper		—		8,249		—		8,249
Corporate debt securities		—		1,961		—		1,961
Total assets measured at fair value	$	53,511	$	22,511	$	—	$	76,022

Schedule of changes in financial instruments measured at fair value using Level 3 inputs

	Fair Value Measurements of
	Level 3 Liabilities
	(in thousands)
Balance at December 31, 2012	$	157
Reclassification to additional paid-in capital upon conversion to common stock warrant		(157)
Balance at December 31, 2013	$	—
Financing derivative		89
Balance at December 31, 2014	$	89

Schedule of antidilutive securities excluded from computations of diluted net loss per common share

	Year Ended December 31,
	2014	2013	2012
Convertible preferred stock	—	—	12,329,330
Warrants to purchase preferred stock	—	—	72,029
Options to purchase common stock	2,677,774	1,820,784	1,030,795
Warrants to purchase common stock	88,545	88,545	—
	2,766,319	1,909,329	13,432,154