Stockholders' Equity (Tables)

12 Months Ended

Dec. 31, 2019

Schedule of Accounting for Share-Based Compensation

The following table summarizes share-based compensation expense (in thousands):


	December 31,
	2019		2018		2017
Share-based compensation expense as a component of:
Research and development expenses	$	9,641	$	8,352	$	14,235
General and administrative expenses	14,874		12,494		10,680
	$	24,515	$	20,846	$	24,915

Schedule of Stock Option Plan Activity

Following is a summary of our stock option plan activity and related information:


	Shares	Weighted Average Exercise Price		Weighted Average Remaining Contractual Term in Years	Aggregate Intrinsic Value (In thousands)
Balance at December 31, 2018	1,736,304	$	66.71	5.47	$	125,858
Granted	338,617	$	116.69
Exercised	(112,011)	$	23.65
Forfeited	(6,531)	$	139.37
Balance at December 31, 2019	1,956,379	$	77.54	5.45	72,002
Exercisable at December 31, 2019	1,454,726	$	61.82	4.42	70,345
Options vested and expected to vest as of December 31, 2019	1,956,379	$	77.54	5.45	$	72,002

Schedule of Stock Option Plan Activity by Exercise Price Range

Following is a further breakdown of the options outstanding as of December 31, 2019:


Range of exercise prices	Options outstanding	Weighted average remaining life in years	Weighted average exercise price	Options exercisable	Weighted average exercise price
$9.96 - $12.81	195,148	1.01	$10.25	195,148	$10.25
$14.47	212,116	2.11	$14.47	198,116	$14.47
$21.92	195,955	3.13	$21.92	195,955	$21.92
$32.00 - $74.42	374,059	4.43	$63.72	374,059	$63.72
$85.79 - $100.38	301,459	6.66	$93.41	239,220	$92.25
$101.15 - $113.76	98,112	7.98	$109.91	46,066	$107.65
$117.97	272,687	9.12	$117.97	56,830	$117.97
$119.30 - $159.01	282,475	8.01	$151.55	129,541	$149.80
$159.81 - $171.28	7,050	8.52	$166.40	2,473	$164.90
$195.91	17,318	8.47	$195.91	17,318	$195.91
	1,956,379	5.45	$77.54	1,454,726	$61.82

Schedule of Stock Option Weighted-Average Assumptions

The assumptions used for the specified reporting periods and the resulting estimates of weighted-average grant date fair value per share of options granted:


	Year Ended December 31,
	2019	2018	2017
Risk-free interest rate	1.4%-2.6%	2.7%-3.0%	2.0%-2.2%
Expected volatility	40%-49%	33%-36%	43%-47%
Expected term	4.6 to 5.9 years	5.1 to 5.8 years	6.5 to 6.8 years

Schedule of Restricted Stock Activity

The following is a summary of our restricted stock activity and related information:


	Shares	Weighted-Average Grant Date Fair Value
Outstanding at December 31, 2018	132,273	$130.63
Granted	118,498	$115.90
Vested	(102,846)	$121.55
Forfeited	(666)	$134.36
Outstanding at December 31, 2019	147,259	$125.11