Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2018

Schedule Of Share Based Compensation Stock Options Activity

The following table summarizes the stock option activity and related information:

	Number of Shares			Weighted Average Exercise Price		Total Intrinsic Value (in thousands)
Outstanding as of December 31, 2016		4,457,251		$	7.14	$	23,258
Granted		706,800		$	24.16	$	15,792
Exercised		(353,612	)	$	7.03		-
Forfeited		(258,620	)	$	9.51		-
Outstanding as of December 31, 2017		4,551,819		$	9.66	$	162,002
Granted		998,603			44.19		-
Exercised		(775,224	)		7.34		31,134
Forfeited		(138,053	)		18.71		3,195
Outstanding as of December 31, 2018		4,637,145		$	17.21	$	48,179
Options vested and exercisable		3,077,195		$	9.21	$	42,503

Schedule of Restricted Stock Number of units

A summary of the Company's RSUs and related information is as follows:

	Number of units			Weighted average grant price
Unvested as of December 31, 2016		-		$	-
Granted		120,000			44.28
Unvested as of December 31, 2017		120,000		$	44.28
Granted		456,559			35.54
Vested and Settled		(938	)		49.14
Forfeited		(7,616	)		49.14
Unvested as of December 31, 2018		568,005	(1)	$	37.18

(1) Includes 128,332 RSUs that have vested but are subject to deferred settlement.

Assumptions for Weighted Average Fair Value of Options Granted

The Company used the Black-Scholes option-pricing model for determining the estimated fair value and stock-based compensation for stock-based awards to employees and the board of directors. The assumptions used in the Black-Scholes option-pricing model were as follows: 

	Year Ended December 31,
	2018	2017	2016
Exercise price	$23.78 - $57.53	$12.81 - $44.28	$5.84 - $13.21
Expected volatility	75.6% - 86.1%	81.2% - 87.0%	85.8% - 91.8%
Risk-free rate of interest	2.56% - 3.04%	2.02% - 2.29%	1.36% - 2.18%
Expected term (years)	5.5 - 7.0	5.5 - 7.0	5.3 - 7.0
Expected dividend yield	-	-	-

Schedule of Employee Service Share-based Compensation, Allocation of Recognized Period Costs

The Company recognized stock-based compensation expense in continuing operations as follows:

	Year Ended December 31,
($ in thousands)	2018		2017		2016
Research and development	$	11,820	$	5,423	$	3,025
General and administrative		16,665		3,178		1,999
Total	$	28,485	$	8,601	$	5,024