Preferred Stock and Stockholders' Equity (Tables)

12 Months Ended

Dec. 31, 2019

Equity [Abstract]

Summary of Shares of Common Stock Reserved for Future Issuance

Shares of common stock reserved for future issuance as of December 31, 2019 are as follows:

Common stock:	(in thousands)
Exercise of outstanding options	23,600
Shares available for grant under stock option plans	8,624
	32,224

Summary of Stock Plan Activity

The following table summarizes all activity under the 2004 Plan and the 2012 Plan:

			Outstanding Options
	Shares Available For Future Grant		Options Shares Subject to Options Outstanding		Weighted- Average Exercise Price		Weighted- Average Remaining Contractual Life	Aggregate Intrinsic Value
	(in thousands)		(in thousands)				(in years)	(in thousands)
Balance at December 31, 2016	7,920		17,663		$	3.63
Increase in shares authorized for grant	4,508		—
Shares granted	(5,282	)	5,282		$	9.90
Shares exercised	—		(2,007	)	$	3.60
Shares canceled and forfeited	484		(484	)	$	5.04
Balance at December 31, 2017	7,630		20,454		$	5.22
Increase in shares authorized for grant	4,589		—
Shares granted	(5,599	)	5,599		$	16.27
Shares exercised	—		(2,121	)	$	4.40
Shares canceled and forfeited	1,106		(1,106	)	$	11.08
Balance at December 31, 2018	7,726		22,826		$	7.72
Increase in shares authorized for grant	4,601
Shares granted	(4,976	)	4,976		$	11.52
Shares exercised	—		(2,929	)	$	3.57
Shares canceled and forfeited	1,273		(1,273	)	$	12.68
Balance at December 31, 2019	8,624		23,600		$	8.77	6.51	$	100,062
Options exercisable at December 31, 2019			15,398		$	6.80	5.45	$	91,283
Options fully vested and expected to vest at December 31, 2019			22,847		$	8.63	6.44	$	99,582

Summary of Options Outstanding and Exercisable

The following is a summary of options outstanding and options exercisable at December 31, 2019.

Options Outstanding											Options Exercisable
Exercise Prices of Options					Number of Shares	Weighted- Average Remaining Contractual Life	Weighted- Average Exercise Price		Aggregate Intrinsic Value		Number of Shares	Weighted- Average Exercise Price		Aggregate Intrinsic Value
					(in thousands)	(in years)			(in thousands)		(in thousands)			(in thousands)
$	1.48	—	$	4.00	6,950	4.2	$	3.02	$	63,079	6,874	$	3.11	$	62,446
$	4.01	—	$	7.00	3,233	4.3	$	5.32	21,974		2,949	$	5.22	20,296
$	7.01	—	$	15.00	9,353	8.3	$	10.73	15,009		3,714	$	9.99	8,541
$	15.01	—	$	24.29	4,064	8.1	$	16.85	—		1,861	$	16.89	—
					23,600	6.5	$	8.77	$	100,062	15,398	$	6.80	$	91,283

Summary of Weighted-Average Assumptions and Resultant Fair Value-Based Measurements for Options Granted to Employees and Directors

The following table summarizes the weighted-average assumptions and resultant fair value-based measurements for options granted to employees and directors.

	Year Ended December 31,
	2019	2018	2017
Weighted-average assumptions for stock options granted:
Risk-free interest rate	2.34%	2.68%	1.99%
Expected term	6.0 years	5.9 years	6.1 years
Expected volatility of stock price	67.4%	67.9%	68.1%
Dividend rate	0%	0%	0%
Weighted-average grant date fair value-based measurement	$7.09	$10.11	$6.14

Summary of Stock-Based Compensation

The following table presents a summary of non-cash stock-based compensation by financial statement classification. 

	Year Ended December 31,
	2019		2018		2017
	(in thousands)
Stock-based compensation capitalized in inventory	$	120	$	87	$	—
Cost of sales	144		259		—
Research and development	9,541		7,012		3,743
Selling, general and administrative	19,628		16,476		9,618
Total stock-based compensation	$	29,433	$	23,834	$	13,361