Stockholders' Equity (Tables)

9 Months Ended

Sep. 30, 2019

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Summary of RSU Activity

The following is a summary of RSU activity under our 2014 EIP and Inducement Plan:

	RSUs
	Shares			Weighted Average Grant Date Fair Value
Unvested as of December 31, 2018		1,405,460		$	26.94
Granted		1,591,888		$	27.04
Forfeited		(435,266	)	$	30.16
Vested		(560,864	)	$	23.89
Outstanding as of September 30, 2019		2,001,218		$	27.17

Summary of Stock Option Activity

The following is a summary of stock option activity under our 2014 EIP and Inducement Plan. The table below also includes the activity relating to options for 275,000 shares of our common stock which were issued in 2017 outside of these plans:

	Shares			Weighted Average Exercise Price		Weighted Average Remaining Contractual Term (Years)		Aggregate Intrinsic Value (in thousands)
Outstanding as of December 31, 2018		6,276,999		$	28.15
Granted		2,100,225			29.86
Exercised		(192,716	)		17.92
Forfeited or expired		(819,920	)		31.74
Outstanding as of September 30, 2019		7,364,588		$	28.51		5.5	$	968
Vested and expected to vest as of September 30, 2019		7,364,588		$	28.51		5.5	$	968
Exercisable as of September 30, 2019		3,284,621		$	25.52		3.5	$	820

Summary of Options Estimated with Weighted Average

The fair value of each option issued was estimated at the date of grant using the Black-Scholes valuation model. The following table summarizes the weighted-average assumptions used as inputs to the Black-Scholes model, and resulting weighted-average grant date fair values of stock options granted to employees during the periods indicated:

	Nine Months Ended September 30,
	2019			2018
Assumptions:
Expected term (years)		5.9			4.6
Expected volatility		76.6	%		73.4	%
Risk-free interest rate		2.2	%		2.7	%
Expected dividend yield		0.0	%		0.0	%
Fair Value:
Weighted-average estimated grant date fair value per share	$	20.03		$	22.86
Options granted		2,100,225			2,633,950
Total estimated grant date fair value	$	42,068,000		$	60,212,000

Schedule of Common Stock Reserved for Future Issuance Under Equity Incentive Plans

The following shares of common stock were reserved for future issuance under our equity incentive plans as of September 30, 2019:

	Total Shares Reserved
2014 Equity Incentive Plan		12,101,764
2018 Inducement Plan		1,213,760
2014 Employee Stock Purchase Plan		1,067,575
Options granted outside the equity plans		109,666
Total reserved shares of common stock		14,492,765

Schedule of Stock-based Compensation, Related to Employee and Nonemployee Stock Awards

Total stock-based compensation expense related to all employee and non-employee stock awards was as follows:

	Three Months Ended September 30,				Nine Months Ended September 30,
	2019		2018		2019		2018
	(in thousands)				(in thousands)
Research and development	$	7,003	$	4,682	$	19,740	$	10,997
General and administrative		5,149		4,570		19,882		13,267
Total stock-based compensation expense	$	12,152	$	9,252	$	39,622	$	24,264