Share-Based Compensation Plans (Tables)

12 Months Ended

Dec. 31, 2019

Share Based Compensation [Abstract]

Weighted Average Assumptions used to Estimate Fair Value of Options Granted

The fair value of each option granted during the periods was estimated on the date of grant using the following weighted average assumptions:

	2019			2018			2017
Expected volatility		64	%		64	%		65	%
Expected term in years		5			6			4
Risk-free interest rate		1.8	%		2.8	%		1.7	%
Dividend yield		0	%		0	%		0	%

Schedule Of Stock Option Activity

A summary of option activity for 2019 is presented below:

	Options			Weighted Average Exercise Price		Weighted Average Remaining Contractual Term (in years)		Aggregate Intrinsic Value
Outstanding at December 31, 2018		18,613,822		$	4.15
Granted		11,579,119			3.00
Exercised		(466,940	)		3.15
Forfeited		(1,186,465	)		3.20
Expired		(1,375,389	)		5.08
Outstanding at December 31, 2019		27,164,147			3.67		7.65	$	19,782,605
Vested or expected to vest at December 31, 2019		27,164,147			3.67		7.65	$	19,782,605
Exercisable at December 31, 2019		11,785,971		$	4.33		5.83	$	3,677,098

Summary Of Non-vested Stock Activity

A summary of non-vested stock activity for 2019 is presented below:

	Nonvested Shares			Weighted Average Grant Date Fair Value
Outstanding at December 31, 2018		2,213,967		$	3.20
Granted		737,682			2.98
Vested		(129,675	)		2.76
Forfeited		(702,163	)		4.14
Outstanding at December 31, 2019		2,119,811		$	2.84

Schedule Of Share-Based Compensation Expense

The impact on our results of operations from share-based compensation for the years ended December 31, 2019, 2018, and 2017, was as follows (in thousands).

	Year Ended
	2019		2018		2017
Research and development	$	3,873	$	3,498	$	6,159
General and administrative		6,019		4,127		6,270
Total share-based compensation expense	$	9,892	$	7,625	$	12,429