Shareholders' Equity (Tables)

9 Months Ended

Sep. 30, 2017

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Summary of Share-based Compensation Expense

Total share-based compensation expense related to all share-based awards for the three and nine months ended September 30, 2017 and 2016 was comprised of the following (in thousands):

	Three Months Ended   September 30,				Nine Months Ended September 30,
	2017		2016		2017		2016
Research and development:
Stock options	$	3,068	$	1,678	$	8,083	$	4,154
Restricted stock	—		—		—		30
Warrants	24		10		58		25
Research and development share-based compensation expense	3,092		1,688		8,141		4,209
General and administrative:
Stock options	2,203		1,666		6,151		4,934
Restricted stock	—		516		409		1,645
Warrants	187		56		475		183
General and administrative share-based compensation expense	2,390		2,238		7,035		6,762
Total share-based compensation expense included in expenses	$	5,482	$	3,926	$	15,176	$	10,971

Stock Options, Valuation Assumptions

The Company estimated the fair value of each stock option grant on the grant date using the Black-Scholes model with the following weighted-average assumptions:

	Nine Months Ended September 30,
	2017		2016
Expected volatility	143	%	141	%
Expected life	6.19 years		5.74 years
Risk-free interest rate	2.0	%	1.3	%
Dividend yield	—		—

Summary of Stock Option Activity

The Company’s 2013 Equity Plan stock option activity for the nine months ended September 30, 2017 was comprised of the following:

	Outstanding Stock Options and 2013 Equity Plan
	Shares Underlying Stock Options		Weighted- Average Exercise Price per Share
Outstanding at December 31, 2016	2,627,462		$	21.07
Granted	1,879,925		$	22.97
Exercised	(152,342	)	$	15.48
Forfeited	(93,608	)	$	21.77
Outstanding at September 30, 2017	4,261,437		$	22.09

Summary of Restricted Stock Activity

The Company’s restricted stock award activity for the nine months ended September 30, 2017 was comprised of the following:

	Number of Shares		Weighted- Average Grant Date Fair Market Value
Unvested at December 31, 2016	542,680		$	13.22
Vested	(542,680	)	$	13.22
Unvested at September 30, 2017	—		$	—