Stockholders' Equity (Tables)

3 Months Ended

Mar. 31, 2020

Equity [Abstract]

Summary of Stock Option Activity

The following table summarizes the stock option activity for the three months ended March 31, 2020:

	Shares (in thousands)			Weighted- average Exercise Price		Weighted- average Remaining Contractual Term (Years)
Balance at December 31, 2019		16,665		$	20.47		7.87
Granted		187		$	20.11
Exercised		(70	)	$	7.20
Expired and forfeited		(272	)	$	22.26
Balance at March 31, 2020		16,510		$	20.49		7.51

Summary of Stock-Based Compensation Expense related to Stock-Based Payment Awards Granted

The following table summarizes stock-based compensation expense related to stock-based payment awards granted pursuant to all of our equity compensation arrangements (in thousands):

	Three Months Ended March 31,
	2020		2019
Research and development	$	5,287	$	5,324
General and administrative		3,431		3,680
Sales and marketing		3,256		8,898
Total stock-based compensation expense	$	11,974	$	17,902

Summary of Fair Value of Option Grant on Grant Date Using Black-Scholes Option Pricing Model

We estimated the fair value of each option grant on the grant date using the Black-Scholes option pricing model with the following weighted-average assumptions:

	March 31,
	2020			2019
Risk-free interest rate		1.3	%		2.5	%
Dividend yield		0.0	%		0.0	%
Volatility		66.2	%		68.8	%
Expected life (years)		6			6