Stockholders' Equity

6 Months Ended

Jun. 30, 2020

Share-based Payment Arrangement [Abstract]

7. Stockholders’ Equity

Stock Repurchase Program

In April 2019, our board of directors authorized a $1.0 billion stock repurchase program (the “Repurchase Program”). This authorization allows us to repurchase shares of our common stock opportunistically and will be funded from working capital. Repurchases may be made at management’s discretion from time to time on the open market, through privately negotiated transactions, transactions structured through investment banking institutions, block purchases, trading plans under Rule 10b5-1 of the Securities Exchange Act of 1934, as amended (the “Exchange Act”), or a combination of the foregoing. The Repurchase Program, which expires in April 2022, does not obligate us to acquire any of our common stock, and may be suspended or discontinued by us at any time without prior notice. As of June 30, 2020, the remaining authorized amount for stock repurchases under this program was approximately $506.0 million.

A summary of the stock repurchase activity under the Repurchase Program for the six months ended June 30, 2020 is as follows (in thousands, except per share amounts):



	Six Months Ended
	June 30, 2020
Aggregate purchase price	$	227,895
Shares repurchased	1,209
Average price paid per share	$	188.61

There was no stock repurchase activity for the three months ended June 30, 2020. The aggregate purchase price of repurchased shares of our common stock is recorded as a reduction to retained earnings. All shares repurchased under the Repurchase Program have been retired.

Equity Award Plan Activities

2014 Equity Incentive Plan

Effective January 1, 2020, the Company's board of directors authorized an increase of 2,291,660 shares to the shares available for issuance under the 2014 Equity Incentive Plan (the “2014 Plan”). Pursuant to the 2014 Plan, the 2020 share increase is determined based on the lesser of 3% of total shares of common stock outstanding as of December 31, 2019, which was,12,500,000 shares, or such amount as determined by our board of directors. As of June 30, 2020, there remained approximately 22.3 million shares available for issuance under the 2014 Plan.

2014 Employee Stock Purchase Plan

Effective January 1, 2020, our board of directors authorized an increase of 763,886 shares to the shares available for issuance under our 2014 Employee Stock Purchase Plan (the “ESPP”). Pursuant to the ESPP, the 2020 share increase was determined based on the lesser of 1% of the total shares of common stock outstanding on December 31, 2019, 2,500,000 shares, or such amount as determined by our board of directors. During the six months ended June 30, 2020, we issued 51,292 shares at a weighted-average purchase price of $184.19 per share under the ESPP. As of June 30, 2020, there remained 3,905,368 shares available for issuance under the ESPP.

Stock Option Activities

The following table summarizes the option activity under our stock plans and related information (in thousands, except years and per share amounts):



	Options Outstanding
	Number of Shares Underlying Outstanding Options		Weighted- Average Exercise Price per Share		Weighted- Average Remaining Contractual Term (Years) of Stock Options	Aggregate Intrinsic Value of Stock Options Outstanding
Balance—December 31, 2019	4,564		$	42.50	4.4	$	740,387
Options granted	—		—
Options exercised	(504	)	25.36
Options canceled	(21	)	159.36
Balance—June 30, 2020	4,039		$	44.03	4.0	$	674,925
Vested and exercisable—June 30, 2020	2,609		$	30.93	3.6	$	467,293

Restricted Stock Unit (RSU) Activities

A summary of the RSU activity under the 2014 Plan and related information are presented below (in thousands, except years and per share amounts):



	Number of Shares		Weighted- Average Grant Date Fair Value Per Share		Weighted-Average Remaining Contractual Term (in years)	Aggregate Intrinsic Value
Unvested balance—December 31, 2019	1,070		$	190.35	1.5	$	217,701
RSUs granted	1,150		213.78
RSUs vested	(246	)	152.85
RSUs forfeited/canceled	(60	)	226.44
Unvested balance—June 30, 2020	1,914		$	208.13	2.0	$	401,996

Shares Available for Grant

The following table presents the stock activity and the total number of shares available for grant under the 2014 Plan as of June 30, 2020 (in thousands):



	Number of Shares
Balance—December 31, 2019	15,146
Authorized	2,292
Options granted	—
RSUs granted	(1,150	)
Options canceled	21
RSUs forfeited	60
Shares traded for taxes	17
Balance—June 30, 2020	16,386

Stock-Based Compensation Expense

Total stock-based compensation expenses related to options, restricted stock units, restricted stock, and employee stock purchase rights granted were allocated as follows (in thousands):



	Three Months Ended June 30,				Six Months Ended June 30,
	2020		2019		2020		2019
Cost of revenue	$	1,585	$	1,028	$	2,912	$	2,126
Research and development	19,378		12,568		35,306		25,699
Sales and marketing	8,277		7,097		14,673		13,631
General and administrative	3,682		3,604		7,587		7,132
Total stock-based compensation	$	32,922	$	24,297	$	60,478	$	48,588

As of June 30, 2020, unrecognized stock-based compensation expenses by award type and their expected weighted-average recognition periods are summarized in the following table (in thousands, except years):



	June 30, 2020
	Stock Option		RSU		ESPP		Restricted Stock
Unrecognized stock-based compensation expense	$	35,043	$	360,713	$	5,793	$	3,206
Weighted-average amortization period	2.9 years		3.7 years		0.9 years		2.2 years