Stockholders' Equity (Tables)

6 Months Ended

Jun. 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		998,567		$	35.17
Forfeited		(346,327	)	$	29.37
Vested		(526,489	)	$	23.69
Unvested as of June 30, 2019		1,531,211		$	32.87
Vested and unreleased		—
Outstanding as of June 30, 2019		1,531,211		$	32.87

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		1,750,825			32.47
Exercised		(181,664	)		18.13
Forfeited or expired		(554,431	)		33.29
Outstanding as of June 30, 2019		7,291,729		$	29.04		5.5	$	8,693
Vested and expected to vest as of    June 30, 2019		7,291,729		$	29.04		5.5	$	8,693
Exercisable as of June 30, 2019		2,972,192		$	24.40		3.5	$	5,697

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:

	Six months ended June 30, 2019			Six months ended June 30, 2018
Assumptions:
Expected term (years)		5.9			4.6
Expected volatility		77.0	%		73.5	%
Risk-free interest rate		2.3	%		2.6	%
Expected dividend yield		0.0	%		0.0	%
Fair Value:
Weighted-average estimated    grant date fair value per share	$	21.82		$	22.79
Options granted		1,750,825			1,578,750
Total estimated grant date fair value	$	38,203,000		$	35,980,000

Schedule of Common Stock Reserved for Future Issuance

The following shares of common stock were reserved for future issuance as of June 30, 2019:

	Total Shares Reserved
2014 Equity Incentive Plan		12,135,316
2018 Inducement Plan		1,223,621
2014 Employee Stock Purchase Plan		1,067,575
Options granted outside the equity plans		109,666
Total reserved shares of common stock		14,536,178

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 June 30,				Six months ended June 30,
	2019		2018		2019		2018
	(in thousands)				(in thousands)
Research and development	$	6,672	$	3,384	$	12,737	$	6,316
General and administrative		8,529		4,614		14,733		8,697
Total stock-based compensation expense	$	15,201	$	7,998	$	27,470	$	15,013