Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2019

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Summary of Stock Option and Related Information

The following table summarizes stock option activity and related information for the periods presented below:

	Shares Subject to Outstanding Options			Weighted Average Exercise Price Per Option		Weighted Average Remaining Contractual Term (in years)		Aggregate Intrinsic Value (in thousands)
Balance at December 31, 2018		3,701,461		$	26.40
Options granted		1,371,130			43.27
Options exercised		(337,846	)		15.78
Options canceled		(160,587	)		38.75
Balance at December 31, 2019		4,574,158		$	31.81		7.7	$	187,879
Exercisable at December 31, 2019		2,380,560		$	23.21		7.0	$	118,246
Vested and expected to vest at December 31, 2019		4,574,158		$	31.81		7.7	$	187,879

Schedule of Assumptions for Black-Scholes Option-Pricing Model Used in Determining Fair Value of Time-Based and Performance-Based Options Granted to Employees

The following table illustrates the assumptions for the Black-Scholes option-pricing model used in determining the fair value of time-based and performance-based options granted to employees:

	Year Ended December 31,
	2019	2018	2017
Risk-free interest rate	1.59% - 2.54%	2.54% - 2.98%	1.92% - 2.27%
Expected life (in years)	6.1%	5.3 - 6.1	5.3 - 6.1
Volatility	65% - 69%	69% - 75%	71% - 75%
Dividend yield	0%	0%	0%

Summary of RSU Activity and Related Information

The following table summarizes RSU activity and related information for the period presented below:

	Shares Subject to Outstanding Awards			Weighted Average Grant Date Fair Value		Weighted Average Remaining Contractual Term (in years)		Aggregate Intrinsic Value (in thousands)
Balance at December 31, 2018		162,946		$	53.37
RSUs awarded		643,814			45.36
RSUs released		(42,214	)		53.08
RSUs forfeited		(23,450	)		48.23
Balance at December 31, 2019		741,096		$	46.59		2.2	$	54,015

Schedule of Stock-Based Compensation Expense, Net of Forfeitures

Stock-based compensation expense, net of forfeitures, as applicable for the years ended December 31, 2019, 2018 and 2017, is reflected in the statements of operations and comprehensive loss as follows (in thousands):

	Year Ended December 31,
	2019		2018		2017
Research and development	$	14,673	$	8,144	$	2,752
Selling, general and administrative	$	18,321		11,197		3,386
Total stock-based compensation	$	32,994	$	19,341	$	6,138