7. Stock-Based Compensation

Restricted Stock Units

During the nine months ended September 30, 2017, the Company granted 32,500 restricted stock units to employees of the Company. The Company did not grant restricted stock units prior to January 1, 2017. During the three and nine months ended September 30, 2017, the Company recorded $0.2 million and $0.4 million, respectively, of stock-based compensation expense related to its restricted stock units. These restricted stock units vest ratably over two years, with cliff vesting of 50% at both the one-year and two-year anniversary of the grant, which will be in February 2018 and February 2019, respectively.

Stock Option Plans

On December 15, 2016, the Board of Directors of the Company approved the 2016 Inducement Equity Plan (the “2016 Stock Option Plan”). The 2016 Stock Option Plan provides for the grant of equity awards to individuals who have not previously been an employee or a non-employee director of the Company to induce them to accept employment and to provide them with a proprietary interest in the Company.

As of September 30, 2017, under the 2014 Stock Option and Incentive Plan (the “2014 Stock Option Plan”) and the 2016 Stock Option Plan, an aggregate of 8,094,060 shares were reserved and 2,125,783 shares were available for future issuance.

The 2014 Stock Option Plan provides for an annual increase, to be added on the first day of each year, of up to 4% of the Company’s issued and outstanding shares of common stock on the last day of the prior year. On January 1, 2017, 1,488,886 shares of common stock, representing 4% of the Company’s issued and outstanding shares of common stock as of December 31, 2016, were added to the 2014 Stock Option Plan.

During the nine months ended September 30, 2017 and 2016, the Company granted 449,208 and 74,039 options, respectively, to employees to purchase shares of common stock that contain performance-based vesting criteria, primarily related to the achievement of certain clinical and regulatory development milestones related to product candidates. Recognition of stock-based compensation expense associated with these performance-based stock options commences when the performance condition is considered probable of achievement, using management’s best estimates.

During the nine months ended September 30, 2017 and 2016, the achievement of the remaining milestones that are the criteria for vesting of performance-based stock options was considered not probable, nor met, and therefore no expense has been recognized related to these awards for the nine months ended September 30, 2017 and 2016.

Stock-based compensation expense for stock options and restricted stock units recognized during the three and nine months ended September 30, 2017 and 2016 was as follows:

	Three months ended September 30,				Nine months ended September 30,
	2017		2016		2017		2016
	(in thousands)
Research and development	$	5,399	$	2,530	$	14,239	$	6,179
General and administrative		4,332		2,218		11,050		6,748
	$	9,731	$	4,748	$	25,289	$	12,927

The weighted average grant date fair value per share relating to outstanding stock options granted under the Company’s stock option plans during the nine months ended September 30, 2017 and 2016 was $40.43 and $23.32, respectively.

The table below summarizes activity related to stock options:

	Shares			Weighted Average Exercise Price		Weighted Average Remaining Life (in years)		Aggregate Intrinsic Value (in thousands)
Outstanding as of December 31, 2016		4,231,807		$	29.99		8.24	$	92,843
Granted		2,169,250			58.33
Exercised		(286,748	)		22.20
Forfeited		(176,132	)		42.57
Outstanding as of September 30, 2017		5,938,177		$	40.35		8.19	$	140,390
Exercisable as of September 30, 2017		2,301,343		$	25.30		7.10	$	85,819

At September 30, 2017, the Company had unrecognized stock-based compensation expense related to its unvested service-based stock option awards of $90.2 million, which is expected to be recognized over the remaining weighted average vesting period of 2.68 years. The total fair value of options vested for the nine months ended September 30, 2017 and 2016 was $18.0 million and $14.9 million, respectively.

At September 30, 2017, 678,252 performance-based stock options were both outstanding and unvested, and the total unrecognized stock-based compensation expense related to those awards was $13.7 million.