Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2015

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, 2015 and 2014 are as follows:

($ in thousands)	Fair Value Measurements at Reporting Date Using
Description	Balance as of December 31, 2015		Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Cash equivalents	$	137,405	$	137,405	$	—	$	—

($ in thousands)	Fair Value Measurements at Reporting Date Using
Description	Balance as of December 31, 2014		Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Cash equivalents	$	37,290	$	37,290	$	—	$	—

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)	2015		2014		2013
Research and development	$	1,403	$	1,416	$	792
General and administrative		6,594		3,327		2,715
Share based employee compensation expense before tax		7,997		4,743		3,507
Income tax benefit		—		—		—
Net share based employee compensation expense	$	7,997	$	4,743	$	3,507

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:

	2015	2014	2013
Weighted average risk-free interest rate	1.46 - 1.93%	1.74 - 2.11%	1.00 - 2.10%
Expected life in years	6	6	6
Expected volatility	79.13 - 86.81%	85.22 - 94.55%	83.40 - 95.96%
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 warrants, 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, 2015, 2014, and 2013 consist of the following:

	December 31,
	2015		2014		2013
Stock options		3,481,468		6,505,664		6,747,303
Unvested restricted stock		1,586,388		144,508		352,865
Warrants		—		—		10,539,767
		5,067,856		6,650,172		17,639,935