SHARE-BASED COMPENSATION (Tables)

12 Months Ended

Dec. 31, 2015

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

Compensation Cost Related to Share Based Compensation

Share-Based Compensation. The compensation cost that has been included in the statement of comprehensive loss for all share-based compensation arrangements is as follows (in thousands):

	Years Ended December 31,
	2015		2014		2013
General and administrative expense	$	15,281	$	5,167	$	3,516
Research and development expense		13,111		5,215		3,303
Share-based compensation expense	$	28,392	$	10,382	$	6,819

Weighted-Average Assumptions for Stock Option Grants using Black-Scholes Option-Pricing Model

common stock on the date of grant. The estimated fair value of each option award granted was determined on the date of grant using the Black-Scholes option-pricing valuation model with the following weighted-average assumptions for option grants during the three years ended December 31, 2015:

	Years Ended December 31,
	2015			2014			2013
Risk-free interest rate		1.7	%		2.2	%		1.4	%
Expected volatility of common stock		66	%		71	%		76	%
Dividend yield		0.0	%		0.0	%		0.0	%
Expected option term		6.6 years			7.2 years			7.3 years

Summary and Changes in Stock Options Outstanding

A summary of the status of the Company’s stock options as of December 31, 2015, 2014 and 2013 and of changes in options outstanding under the plans during the three years ended December 31, 2015 is as follows (in thousands, except for weighted average exercise price data):

	2015					2014					2013
	Options			Weighted Average Exercise Price		Options			Weighted Average Exercise Price		Options			Weighted Average Exercise Price
Outstanding at January 1		5,750		$	9.31		5,853		$	7.54		6,166		$	7.62
Granted		1,159			37.21		1,089			18.41		771			9.24
Exercised		(1,315	)		5.01		(1,135	)		6.50		(904	)		5.96
Canceled		(87	)		46.08		(57	)		56.83		(180	)		25.68
Outstanding at December 31		5,507		$	15.63		5,750		$	9.31		5,853		$	7.54

Summary and Changes in Restricted Stock Units Outstanding

A summary of the status of the Company’s RSUs as of December 31, 2015, 2014 and 2013 and of changes in RSUs outstanding under the plans for the three years ended December 31, 2015 is as follows (in thousands, except for weighted average grant date fair value per unit):

	2015					2014					2013
	Number of Units			Weighted Average Grant Date Fair Value per Unit		Number of Units			Weighted Average Grant Date Fair Value per Unit		Number of Units			Weighted Average Grant Date Fair Value per Unit
Outstanding at January 1		669		$	15.01		373		$	8.65		—		$	—
Granted		448			33.62		389			19.59		379			8.65
Cancelled		(16	)		20.83		—			—		(6	)		8.65
Converted into common shares		(191	)		14.24		(93	)		8.65		—			—
Outstanding at December 31		910		$	24.23		669		$	15.01		373		$	8.65