SHARE-BASED COMPENSATION (Tables)

6 Months Ended

Jun. 30, 2018

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 thousands):

	Three Months Ended June 30,				Six Months Ended June 30,
	2018		2017		2018		2017
General and administrative	$	7,572	$	6,250	$	14,828	$	11,703
Research and development		4,279		3,640		16,902		7,163
Total share-based compensation expense	$	11,851	$	9,890	$	31,730	$	18,866

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,
	2018	2017	2018	2017
Risk-free interest rate	2.8%	1.9%	2.5%	2.0%
Expected volatility of common stock	57.7%	58.5%	60.1%	58.1%
Dividend yield	0.0%	0.0%	0.0%	0.0%
Expected option term	5.4 years	5.6 years	4.8 years	5.7 years