SHARE-BASED COMPENSATION (Tables)

6 Months Ended

Jun. 30, 2014

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Compensation Expenses Related to Share Based Compensation

The compensation expense related to the Company’s share-based compensation arrangements has been included in the condensed consolidated statements of comprehensive loss as follows (in millions):

	Three Months Ended June  30,				Six Months Ended June  30,
	2014		2013		2014		2013
General and administrative	$	1.4	$	0.9	$	2.6	$	1.7
Research and development		1.5		0.8	$	2.7	$	1.7
Total share-based compensation expense	$	2.9	$	1.7	$	5.3	$	3.4

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

The estimated fair value of each stock option granted was determined on the date of grant using the Black-Scholes option-pricing model with the following weighted-average assumptions for the stock option grants:

	Three Months Ended June 30,		Six Months Ended June 30,
	2014	2013	2014	2013
Risk-free interest rate	2.1%	1.5%	2.3%	1.4%
Expected volatility of common stock	70.6%	77.5%	71.2%	75.8%
Dividend yield	0.0%	0.0%	0.0%	0.0%
Expected option term	7.3 years	7.5 years	7.1 years	7.3 years