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Stock-based Compensation (Tables)

12 Months Ended

Dec. 31, 2020

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Summary of Recognized Stock-Based Compensation

The Company recognized stock-based compensation as follows:

		Year Ended December 31,
		2020				2019				2018
		(In thousands)
Research and development		$	14,980			$	8,031			$	4,195
General and administrative			15,542				8,250				2,730
Total stock-based compensation		$	30,522			$	16,281			$	6,925

Summary of Share-based Payment Award, Stock Options, Valuation Assumptions

The estimated grant-date fair value of all the Company’s options to purchase common stock was calculated using the Black-Scholes option pricing model, based on the following assumptions:

		Year Ended December 31,
		2020			2019			2018
Expected term (in years)		5.3-6.1			5.3 – 6.1			5.1 – 6.1
Expected volatility		74%-78%			76% – 82%			73% – 81%
Risk-free interest rate		0.3% - 1.8%			1.4% – 2.6%			2.5% – 3.1%
Dividend yield		0%			0%			0%

Summary of Restricted Common Stock

Activity for the restricted common stock is shown below:

		Number of Shares				Weighted Average Grant Date Fair Value per Share
Unvested restricted common stock as of    December 31, 2018			1,917,848			$	6.95
Vested			(866,037	)			6.95
Forfeited			(56,973	)			6.95
Unvested restricted common stock as of    December 31, 2019			994,838				6.95
Vested			(726,659	)			6.95
Forfeited			(81,754	)			6.95
Unvested restricted common stock as of    December 31, 2020			186,425				6.95

Summary of Options to Purchase Common Stock

Activity for the options to purchase common stock shown below:

		Number of Options				Weighted Average Exercise Price Per Share				Weighted Average Remaining Contractual Term				Aggregate Intrinsic Value
										(In years)				(In thousands)
Outstanding as of December 31, 2018			5,063,688			$	8.94
Granted			3,738,071				17.74
Exercised			(180,287	)			8.43
Forfeited			(178,648	)			11.52
Outstanding as of December 31, 2019			8,442,824				12.79
Granted			5,597,148				15.35
Exercised			(655,772	)			9.65
Forfeited			(729,202	)			14.96
Outstanding as of December 31, 2020			12,654,998			$	13.96				8.7			$	39,633
Exercisable as of December 31, 2020			3,588,568			$	12.74				8.1			$	13,393
Vested and expected to vest as of December 31,    2020			12,654,998			$	13.96				8.7			$	39,633

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Tabular disclosure of allocation of amount expensed and capitalized for award under share-based payment arrangement to statement of income or comprehensive income and statement of financial position. Includes, but is not limited to, corresponding line item in financial statement.

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Tabular disclosure of the changes in outstanding nonvested restricted stock units.

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Tabular disclosure for stock option plans. Includes, but is not limited to, outstanding awards at beginning and end of year, grants, exercises, forfeitures, and weighted-average grant date fair value.

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