Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2015

Allocation of Stock-Based Compensation Expense for Employee and Non-Employee Stock Options and Restricted Stock in Statements of Operations

During the years ended December 31, 2015, 2014 and 2013, the Company recorded stock-based compensation expense, which was allocated as follows in the statements of operations (in thousands):



	Year Ended December 31,
	2015		2014		2013
Research and development expense	$	1,032	$	1,069	$	1,150
General and administrative expense	1,497		1,363		110
	$	2,529	$	2,432	$	1,260

Summary of Assets and Liabilities Measured at Fair Value on Recurring Basis

The following table presents information about the Company’s financial assets and liabilities that have been measured at fair value, and indicates the fair value hierarchy of the valuation inputs utilized to determine such fair value. The Company determines the fair value of the common stock warrants (See Note 9) using Level 3 inputs.

The following table summarizes the assets and liabilities measured at fair value on a recurring basis at December 31, 2015 (in thousands):



Description	December 31, 2015		Active Markets (Level 1)		Observable Inputs (Level 2)		Unobservable Inputs (Level 3)
Assets:
Cash and cash equivalents	$	36,079	$	36,079
Restricted cash	94		94
Total assets	$	36,173	$	36,173	$	—	$	—
Liabilities:
Warrant liability	$	115	$	—	$	—	$	115
Total liabilities	$	115	$	—	$	—	$	115

The following table summarizes the assets and liabilities measured at fair value on a recurring basis at December 31, 2014 (in thousands):



Description	December 31, 2014		Active Markets (Level 1)		Observable Inputs (Level 2)		Unobservable Inputs (Level 3)
Assets:
Cash and cash equivalents	$	54,059	$	54,059	$	—	$	—
Restricted cash	94		94		—		—
Total assets	$	54,153	$	54,153	$	—	$	—
Liabilities:
Warrant liability	$	3,219	$	—	$	—	$	3,219
Total liabilities	$	3,219	$	—	$	—	$	3,219

Summary of Changes in the Fair Value of the Company's Preferred Stock Warrant Liability

The following table sets forth a summary of changes in the fair value of the Company’s common stock warrant liability, which represented a recurring measurement classified within Level 3 of the fair value hierarchy, wherein fair value was estimated using significant unobservable inputs (in thousands):



Beginning balance, January 1, 2015	$	3,219
Change in fair value of common stock warrants	(3,104		)
Ending balance, December 31, 2015	$	115

Summary of Common Stock Equivalents Excluded from Calculation of Diluted Net Loss Per Share

The following common stock equivalents were excluded from the calculation of diluted net loss per share applicable to common stockholders for the periods indicated because including them would have had an anti-dilutive effect or the exercise prices were greater than the average market price of the common shares.



	As of December 31,
	2015	2014	2013
Convertible preferred stock	—	—	8,260,444
Stock options	1,803,574	1,438,528	1,346,238
Unvested restricted stock	41,657	125,027	163,353
Restricted stock units	150,932	—	—
Common stock warrants	926,840	899,340	333,799
Preferred stock warrants	—	—	30,708
	2,923,003	2,462,895	10,134,542