STOCK BASED COMPENSATION (Tables)

6 Months Ended

Jun. 30, 2015

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Summary of Options Issued Under the Plan

A summary of the status of the options issued under the Plan as of June 30, 2015, and information with respect to the changes in options outstanding is as follows:

				OPTIONS OUTSTANDING
									WEIGHTED-
							WEIGHTED-		AVERAGE
	SHARES			OUTSTANDING			AVERAGE		REMAINING		AGGREGATE
	AVAILABLE			STOCK			EXERCISE		CONTRACTUAL		INTRINSIC
	FOR GRANT			OPTIONS			PRICE		LIFE (YEARS)		VALUE
Balance at January 1, 2015		1,009,150			5,338,707		$	14.01		9.2	$	64,704,526
Authorized under the Plans		2,201,772			—			—
Granted under the Plans		(1,842,000	)		1,842,000			60.44
Exercised		—			(290,695	)		3.10
Surrendered/Cancelled		210,001			(210,001	)		60.29
Balance at June 30, 2015		1,578,923			6,680,011		$	21.15		9.0	$	237,459,824
Exercisable at June 30, 2015					1,628,142		$	3.81		8.3	$	93,093,140

Schedule of Black-Scholes Option Pricing Model

The fair value of each stock option granted has been determined using the Black-Scholes option pricing model. The material factors incorporated in the Black-Scholes model in estimating the fair value of the options granted during the six months ended June 30, 2015 and 2014 included the following:

	SIX MONTHS ENDED JUNE 30,
	2015		2014
Risk-free interest rate	1.19% - 1.75%		1.62% - 1.72%
Expected volatility	72.0% - 80.0%		74.5% - 76.4%
Stock price	$50.02 - $72.42		$1.35 - $17.00
Expected life	6 years		6 years
Expected dividend yield		0%		0%

Summary of Stock-Based Compensation

Stock-based compensation for the three and six months ended June 30, 2015 and 2014 is as follows (in thousands):

	THREE MONTHS ENDED				SIX MONTHS ENDED
	JUNE 30,				JUNE 30,
	2015		2014		2015		2014
Research and development	$	4,765	$	4,760	$	7,544	$	4,806
General and administrative		4,616		2,284		8,514		2,435
Total	$	9,381	$	7,044	$	16,058	$	7,241

Schedule of Stock Options Outstanding

The following table summarizes information about stock options outstanding as of June 30, 2015:

	OUTSTANDING						EXERCISABLE
			WEIGHTED-
			AVERAGE		WEIGHTED-				WEIGHTED-
			REMAINING		AVERAGE				AVERAGE
EXERCISE PRICE	TOTAL SHARES		CONTRACTUAL LIFE		EXERCISE PRICE		TOTAL SHARES		EXERCISE PRICE
0.38		346,542		6.6	$	0.38		281,542	$	0.38
0.70		956,543		8.4		0.70		617,688		0.70
1.35		1,180,377		8.7		1.35		410,886		1.35
6.89		837,092		8.9		6.89		182,117		6.89
17.00 - 32.56		868,157		9.2		26.06		94,659	17.00
40.30 - 51.96		779,300		9.4		50.16		30,000	51.43
53.90 - 59.23		730,000		9.6		54.89		1,875	54.47
60.61 - 65.50		847,000		9.7		63.97		9,375	63.52
71.45		125,000		9.5		71.45		—		—
72.42		10,000		9.6		72.42		—		—
Total		6,680,011		9.0	$	21.15		1,628,142	$	3.81