Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2017

Assets and Liabilities Measured at Fair Value on Recurring Basis

Assets and liabilities measured at fair value on a recurring basis as of December 31, 2017 and 2016 are as follows:


($ in thousands)				Fair Value Measurements at Reporting Date Using
Description	Balance as of December 31, 2017			Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Cash equivalents	$	66,156		$	66,156	$	—	$	—

Derivative liabilities	$	(2,424	)	$	—	$	—	$	(2,424	)


($ in thousands)				Fair Value Measurements at Reporting Date Using
Description	Balance as of December 31, 2016			Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Cash equivalents	$	77,120		$	77,120	$	—	$	—

Derivative liabilities	$	(862	)	$	—	$	—	$	(862	)

Share-Based Compensation Expense Included in Statements of Operations

The following table presents share-based compensation expense included in the Company’s Statements of Operations:


	Year ended December 31,
(in thousands)	2017		2016		2015
Research and development	$	2,401	$	2,077	$	1,403
General and administrative		6,053		6,375		6,594

Share based employee compensation expense before tax		8,454		8,452		7,997
Income tax benefit		—		—		—

Net share based employee compensation expense	$	8,454	$	8,452	$	7,997

Assumptions for Volatility, Expected life, Dividend Yield and Risk-free Interest Rate

The assumptions for volatility, expected life, dividend yield and risk-free interest rate are presented in the table below:


	2017	2016	2015
Weighted average risk-free interest rate	1.85 - 2.27%	1.27 - 2.09%	1.46 - 1.93%
Expected life in years	6	6	6
Expected volatility	80.31 - 81.03%	79.15 - 82.95%	79.13 - 86.81%
Expected dividend yield	0	0	0

Potentially Dilutive Shares Excluded from Computation of Diluted Net Loss Per Share

The Company’s potentially dilutive shares, which include outstanding common stock options, unvested restricted stock and preferred stock, have not been included in the computation of diluted net loss per share for any of the periods presented as the result would be antidilutive. Such potential common shares at December 31, 2017, 2016, and 2015 consist of the following:


	December 31,
	2017		2016		2015
Stock options		4,352,135		3,465,335		3,481,468
Unvested restricted stock		1,808,559		1,680,492		1,586,388
Preferred stock		34,134,524		20,465,067		—

	40,295,218		25,610,894		5,067,856