The Company maintains four equity compensation plans that provide for the issuance of shares of the Company’s common stock to its officers and other employees, directors, and consultants: the 2010 Stock Plan (the “2010 Plan”), the 2013 Equity Incentive Plan (the “2013 Plan”), the 2019 Equity Incentive Plan (the “2019 Plan”), and the 2019 Employee Stock Purchase Plan (the “ESPP”), which have all been approved by stockholders. Following the Company’ initial public offering (“IPO”), the Company has only issued awards under the 2019 Plan and the ESPP, and no additional awards will be granted under the 2010 and 2013 Plans. These plans provide for the issuance of incentive stock options (“ISOs”), nonqualified stock options (“NSOs”), stock appreciation rights (“SARs”), restricted stock, restricted stock units (“RSUs”), performance-based awards, and other awards (that are based in whole or in part by reference to the Company’s common stock).

A summary of stock option and SAR activity for the three months ended March 31, 2020 is as follows (in millions, except share amounts which are reflected in thousands, per share amounts, and years):



	SARs Outstanding Number of SARs		Options Outstanding Number of Shares		Weighted-Average Exercise Price Per Share		Weighted-Average Remaining Contractual Life (in years)	Aggregate Intrinsic Value
As of December 31, 2019	337		34,801		$	9.79	4.75	$	746
Granted	—		1,194		11.55
Exercised	(2	)	(4,490	)	3.06
Canceled and forfeited	(24	)	(220	)	21.14
As of March 31, 2020	311		31,285		$	10.72	4.68	$	599
Vested and expected to vest as of March 31, 2020	198		25,331		$	5.41	4.31	$	585
Exercisable as of March 31, 2020	198		25,331		$	5.41	4.31	$	585



	Number of Shares		Weighted-Average Grant-Date Fair Value per Share
Unvested and outstanding as of December 31, 2019	84,743		$	39.82
Granted	43,229		$	22.91
Vested	(8,949	)	$	41.49
Canceled and forfeited	(3,817	)	$	41.32
Unvested and outstanding as of March 31, 2020	115,206		$	34.03

Stock-based compensation expense is allocated based on the cost center to which the award holder belongs. The following table summarizes total stock-based compensation expense by function for the three months ended March 31, 2019 and 2020 (in millions):

As of March 31, 2020, there was $2.7 billion of unamortized compensation costs related to all unvested awards. The unamortized compensation costs are expected to be recognized over a weighted-average period of approximately 2.81 years.

The tax benefits recognized in the condensed consolidated statements of operations for stock-based compensation arrangements were not material during the three months ended March 31, 2019 and 2020, respectively.