Stock-Based Compensation (Tables)

3 Months Ended

Mar. 31, 2021

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Schedule of Recorded Stock-Based Compensation Expense

Stock-based compensation expense was recorded directly to research and development and selling, general and administrative expense as follows (in thousands):

	Three Months Ended March 31,
	2021		2020
Research and development	$	12,221	$	10,637
Selling, general and administrative		7,163		6,279
Total stock-based compensation expense	$	19,384	$	16,916

Schedule of Assumptions used to Estimate Fair Value of Stock Options Granted and Purchases under 2014 Employee Share Purchase Plan

The assumptions used to estimate the fair value of stock options granted and purchases under the Company’s 2014 Employee Share Purchase Plan (“ESPP”) using the Black-Scholes option valuation model were as follows:

	Three Months Ended March 31,
	2021			2020
Stock Options
Expected term (in years)		5.7			5.7
Expected volatility		58.8	%		68.3	%
Risk-free interest rate		0.7	%		0.9	%
Expected dividend yield		—			—
Weighted average estimated fair value	$	27.46		$	17.24

ESPPs
Expected term (in years)	0.5 - 2.0			0.5 - 2.0
Expected volatility	47.5 - 64.4		%	49.5 - 57.7		%
Risk-free interest rate	0.1 - 2.2		%	1.5 - 2.9		%
Expected dividend yield		—			—
Weighted average estimated fair value	$	16.94		$	18.57