Share-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2020

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Summary of Performance-Based Option Activity

Performance-based option activity under the 2007 SIP, the 2013 SIP, and the 2018 EIP was as follows:

	Shares			Weighted Average Exercise Price (per share)			Weighted Average Remaining Contractual Term (in years)		Aggregate Intrinsic Value (in millions)
Performance-based options outstanding at December 31, 2017		1,038,147		$	13.46			3.5	$	—
Granted		—			—			—		—
Exercised		(663,412	)		(13.46	)		—		—
Forfeited or expired		(8,358	)		(13.46	)		—		—
Performance-based options outstanding at December 31, 2018		366,377		$	13.50			3.1	$	7.7
Granted		—			—			—		—
Exercised		(298,096	)		(13.48	)		—		—
Forfeited or expired		—			—			—		—
Performance-based options outstanding at December 31, 2019		68,281		$	13.58			2.6	$	3.7
Granted		1,818,728			65.27			—		—
Exercised		(42,730	)		(13.46	)		—		—
Forfeited or expired		—			—			—		—
Performance-based options outstanding at December 31, 2020		1,844,279		$	64.55			9.2	$	77.5
Performance-based options exercisable at December 31, 2020		25,551		$	13.78			1.7	$	2.4

Summary of Term-Based Stock Option Activity

Term-based stock option activity under the 2007 SIP, the 2013 SIP, and the 2018 EIP, was as follows:

	Shares			Weighted Average Exercise Price (per share)			Weighted Average Remaining Contractual Term (in years)		Aggregate Intrinsic Value (in millions)
Term-based options outstanding at December 31, 2017		10,994,181		$	16.52			6.9	$	48.8
Granted		5,236,037			23.07			—		—
Exercised		(2,501,983	)		(15.26	)		—		—
Forfeited or expired		(178,466	)		(17.30	)		—		—
Term-based options outstanding at December 31, 2018		13,549,769		$	19.28			7.5	$	206.8
Granted		4,297,472			49.74			—		—
Exercised		(4,358,867	)		(17.37	)		—		—
Forfeited or expired		(343,437	)		(24.14	)		—		—
Term-based options outstanding at December 31, 2019		13,144,937		$	29.74			7.8	$	501.3
Granted		2,282,334			66.06			—		—
Exercised		(3,889,096	)		(20.42	)		—		—
Forfeited or expired		(555,101	)		(32.09	)		—		—
Term-based options outstanding at December 31, 2020		10,983,074		$	40.47			7.8	$	725.9
Term-based options exercisable at December 31, 2020		3,085,305		$	28.50			6.8	$	240.9

Other Information Pertaining to Term-Based Options

Other information pertaining to term-based options was as follows:

	Year Ended December 31,
	2020		2019		2018
Weighted average grant date fair value per share	$	21.15	$	16.12	$	7.80

Fair Value of Stock Option Estimated Using Black-Scholes Option Pricing Model

The fair value of the term-based stock options was estimated at the date of grant using the Black-Scholes option pricing model with the following weighted-average assumptions:

	Year Ended December 31,
	2020			2019			2018
Expected volatility		29.8	%		24.9	%		25.0	%
Expected dividend rate		—			—			—
Risk-free interest rate		0.6	%		2.5	%		2.9	%

Summary of Restricted Stock Units Activity

RSU activity under the 2013 SIP and the 2018 EIP, was as follows:

	Shares
RSUs outstanding at December 31, 2017		605,990
Granted		164,073
Shares issued upon vesting of RSUs		(105,990	)
Forfeited or canceled		—
RSUs outstanding at December 31, 2018		664,073
Granted		193,033
Shares issued upon vesting of RSUs		(17,288	)
Forfeited or canceled		(20,000	)
RSUs outstanding at December 31, 2019		819,818
Granted		685,997
Shares issued upon vesting of RSUs		(73,475	)
Forfeited or canceled		(42,955	)
RSUs outstanding at December 31, 2020		1,389,385
RSUs releasable at December 31, 2020		423,479

Other Information Pertaining to RSUs

Other information pertaining to RSUs was as follows:

	Year Ended December 31,
	2020		2019		2018
Weighted average grant date fair value per share	$	69.57	$	50.00	$	35.55

Summary of Global Employee Stock Purchase Plan Activity

Our GESPP activity was as follows:

	Year Ended December 31,
	2020		2019
Shares issued		182,899		261,895
Purchase price (per share)	$	54.90	$	28.70

Summary of Fair Value of Stock Purchase Rights Granted under the Global Employee Stock Purchase Plan Estimated Using Weighted-Average Assumptions

The fair value of the stock purchase rights granted under the GESPP was estimated using the following weighted-average assumptions:

	Year Ended December 31, 2020			Year Ended December 31, 2019
Expected volatility		46.4	%		34.8	%
Expected dividend rate		—			—
Risk-free interest rate		1.1	%		2.2	%
Expected term (in years)		0.3			0.4
Grant date fair value per share	$	17.11		$	9.32