Share-Based Payments (Tables)

12 Months Ended

Dec. 31, 2018

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Summary of share-based compensation expense (income)

The following table summarizes share-based compensation expense recorded in each of the years ended December 31, 2018, 2017 and 2016 (in thousands):

	2018		2017		2016
Stock options	$	7,081	$	10,036	$	9,831
Restricted stock awards and restricted stock units	10,032		5,608		8,064
Employee stock purchase plan	301		483		427
Restructuring	3,808		—		—
Total share-based compensation expense	$	21,222	$	16,127	$	18,322

The table below presents share-based compensation expense for research and development as well as general and administrative expense, both of which are included in operating expenses, in the years ended December 31, 2018, 2017 and 2016 (in thousands):

	2018		2017		2016
Research and development	$	6,383	$	5,699	$	7,558
General and administrative	11,031		10,428		10,764
Restructuring	3,808		—		—
Total share-based compensation expense	$	21,222	$	16,127	$	18,322

Schedule of weighted average assumptions

The following table summarizes the weighted average assumptions the Company used in its fair value calculations at the date of grant:

	Weighted Average Assumptions
	Stock Options						Employee Stock Purchase Plan
	2018		2017		2016		2018		2017		2016
Expected volatility	48	%	53	%	58	%	49	%	55	%	57	%
Expected dividends	—		—		—		—		—		—
Expected life (years)	6.1		5.9		6.1		0.5		0.5		0.5
Risk-free interest rate	2.8	%	2.1	%	1.6	%	1.6	%	0.7	%	0.4	%

Schedule of stock option activity of company's stock plan

The following table presents stock option activity for the year ended December 31, 2018:

	Number of Stock Options (in thousands)		Weighted Average Exercise Price		Weighted Average Remaining Contractual Term (in years)	Aggregate Intrinsic Value (in thousands)
Outstanding at December 31, 2017	7,117		$	14.71
Granted	373		19.63
Exercised	(1,995	)	14.12
Forfeited	(476	)	15.53
Expired	(61	)	16.39
Outstanding at December 31, 2018	4,958		$	15.22	4.86	$	407,629
Exercisable at December 31, 2018	3,662		$	14.65	4.03	$	339,688
Vested or expected to vest at December 31, 2018	4,837		$	15.16	4.76	$	404,503

Schedule of nonvested shares of restricted stock

A summary of the status of nonvested shares of restricted stock and restricted stock units as of December 31, 2018 and the changes during the year then ended are presented below (in thousands, except fair values):

	Number of Shares		Weighted Average Grant Date Fair Value
Nonvested at January 1, 2018	1,995		$	12.60
Granted	3,170		14.83
Vested	(959	)	14.03
Forfeited	(707	)	13.25
Nonvested at December 31, 2018	3,499		$	14.10

Summarized information about time-based or performance-based vesting schedules

Nonvested shares of restricted stock and restricted stock units that have time-based vesting schedules and restricted stock that have performance-based vesting schedules as of December 31, 2018 are summarized below (in thousands):

Vesting Schedule	Nonvested Shares
Time-based	1,142
Performance-based	2,357
Nonvested at December 31, 2018	3,499