STOCK-BASED COMPENSATION (Tables)

9 Months Ended

Sep. 30, 2014

Summary of Stock Option Activity

The following table summarizes the Company’s stock option activity for each of the periods indicated:

	For the Three Months Ended September 30,										For the Nine Months Ended September 30,
	2014					2013					2014					2013
	Shares			Weighted Average Exercise Price		Shares			Weighted Average Exercise Price		Shares			Weighted Average Exercise Price		Shares			Weighted Average Exercise Price
Grants outstanding at beginning of the period		5,228,373		$	24.56		3,976,189		$	21.82		4,190,367		$	23.46		2,522,522		$	11.76
Granted		237,050			21.98		309,226			39.17		1,540,085			26.61		2,063,396			34.86
Exercised		(4,742	)		8.85		(76,465	)		8.76		(79,346	)		11.69		(196,012	)		8.51
Canceled or expired		(331,462	)		21.19		(58,116	)		20.62		(521,887	)		22.63		(239,072	)		11.51
Grants outstanding at end of the period		5,129,219		$	24.67		4,150,834		$	23.37		5,129,219		$	24.67		4,150,834		$	23.37
Grants exercisable at end of the period		1,859,285		$	18.61		891,157		$	11.60		1,859,285		$	18.61		891,157		$	11.60

Summary of Restricted Stock Award Activity

The following table summarizes the Company’s RSA activity for each of the periods indicated:

	For the Three Months Ended September 30,									For the Nine Months Ended September 30,
	2014				2013					2014					2013
	Shares		Weighted Average Grant Date Fair Value		Shares			Weighted Average Grant Date Fair Value		Shares			Weighted Average Grant Date Fair Value		Shares			Weighted Average Grant Date Fair Value
Grants outstanding at beginning of the period		6,000	$	29.03		10,998		$	23.63		6,000		$	34.92		4,998		$	10.08
Granted		—		—		—			—		6,000			29.03		6,000			34.92
Vested		—		—		(4,998	)		10.08		(6,000	)		34.92		(4,998	)		10.08
Grants outstanding at end of the period		6,000	$	29.03		6,000		$	34.92		6,000		$	29.03		6,000		$	34.92

Summary of Restricted Stock Unit Activity

The following table summarizes the Company’s RSU activity for each of the periods indicated:

	For the Three Months Ended September 30,									For the Nine Months Ended September 30,
	2014				2013					2014					2013
	Shares		Weighted Average Grant Date Fair Value		Shares			Weighted Average Grant Date Fair Value		Shares			Weighted Average Grant Date Fair Value		Shares			Weighted Average Grant Date Fair Value
Grants outstanding at beginning of the period		—	$	—		13,325		$	5.40		6,507		$	5.40		38,260		$	6.32
Vested		—		—		(264	)		5.40		(6,507	)		5.40		(24,858	)		6.81
Canceled or expired		—		—		(33	)		5.40		—			—		(374	)		5.40
Grants outstanding at end of the period		—	$	—		13,028		$	5.40		—		$	—		13,028		$	5.40

Summary of Stock Appreciation Rights Activity

The following table summarizes the Company’s SAR activity for each of the periods indicated:

	For the Three and Nine Months Ended September 30,
	2014				2013
	Shares		Weighted Average Exercise Price		Shares		Weighted Average Grant Date Fair Value
Grants outstanding at beginning of the period		170,000	$	18.18		170,000	$	18.18
Grants outstanding at end of the period		170,000	$	18.18		170,000	$	18.18
Grants exercisable at end of the period		82,291	$	17.75		18,958	$	10.08

Summary of Stock-Based Compensation Expense by Function Included within Condensed Consolidated Statement of Operations and Comprehensive Loss

The following table summarizes stock-based compensation expense by function included within the unaudited condensed consolidated statements of operations and comprehensive loss:

	For the Three Months Ended September 30,				For the Nine Months Ended September 30,
	2014		2013		2014		2013
	(in thousands)
Research and development	$	1,668	$	1,155	$	5,886	$	2,409
General and administrative		2,981		2,332		8,692		5,067
Total	$	4,649	$	3,487	$	14,578	$	7,476

Summary of Stock-Based Compensation Expense by Grant Type Included within Condensed Consolidated Statement of Operations and Comprehensive Loss

The following table summarizes stock-based compensation expense by grant type included within the unaudited condensed consolidated statements of operations and comprehensive loss:

	For the Three Months Ended September 30,				For the Nine Months Ended September 30,
	2014		2013		2014		2013
	(in thousands)
Stock options	$	4,217	$	2,980	$	13,170	$	6,413
Restricted stock awards		33		58		169		97
Restricted stock units		—		22		1		250
Stock appreciation rights		147		153		440		442
Employee stock purchase plan		252		274		798		274
Total	$	4,649	$	3,487	$	14,578	$	7,476

Stock Options [Member]

Assumptions for Measuring Fair Values of Stocks

The fair values of stock options granted during the periods presented were measured on the date of grant using the Black-Scholes-Merton option-pricing model, with the following assumptions:

	For the Three Months Ended September 30,		For the Nine Months Ended September 30,
	2014	2013	2014	2013
Risk-free interest rate(1)	1.5 – 1.7%	0.7 – 1.4%	1.5 – 1.7%	0.7 – 1.4%
Expected dividend yield(2)	0%	0%	0%	0%
Expected lives(3)	4.7 – 4.8 years	4.9 – 5.0 years	4.7 – 4.9 years	4.9 – 5.0 years
Expected volatility(4)	96.7 – 103.0%	80.0 – 88.9%	93.0 – 103.0%	80.0 – 88.9%

(1) The risk-free interest rate is estimated using an average of Treasury bill interest rates over a historical period commensurate with the expected term of the option that correlates to the prevailing interest rates at the time of grant.

(2) The expected dividend yield is zero as the Company has not paid any dividends to date and does not expect to pay dividends in the future.

(3) The expected lives are estimated using expected and historical exercise behavior.

(4) The expected volatility is estimated using a blend of calculated volatility of the Company’s common stock over a historical period and implied volatility in exchange-traded options of the Company’s common stock.