Incentive Plans (Tables)

3 Months Ended

Mar. 31, 2021

Incentive Plans

Schedule of Valuation Assumptions

	Expected Stock Price		Risk-Free Interest
Award Date	Volatility		rate
February 19, 2020	22	%	1.39	%
February 20, 2020	22	%	1.35	%
January 1, 2021	27	%	0.17	%
February 25, 2021	26	%	0.31	%

Schedule of Deferred Compensation

Below is a summary of our compensation expense for the three months ended March 31, 2021 and 2020 and our unearned compensation as of March 31, 2021 and December 31, 2020 (in millions):

													Expected
													period to
	Deferred Compensation								Unearned Compensation				recognize
	Expensed				Capitalized				As of		As of		unearned
	Three Months Ended March 31,								March 31,		December 31,		compensation
Type of incentive award	2021		2020		2021		2020		2021		2020		(in years)
Long-term incentive units	$	4.2	$	3.1	$	0.1	$	0.1	$	26.7	$	15.1	2.5
Performance-based awards		6.2		4.7		0.4		0.2		52.9		34.4	2.5
Service-based restricted stock units		6.0		3.2		0.7		0.8		64.9		41.5	3.0
Interxion awards		10.5		3.0		—		—		16.4		27.2	2.1

Summary of Long-Term Incentive Unit Activity

		Weighted-Average
		Grant Date Fair
Unvested Long-term Incentive Units	Units	Value
Unvested, beginning of period	235,535	$	122.22
Granted	119,418		136.27
Vested	(105,662)		119.69
Cancelled or expired	(1,016)		128.38
Unvested, end of period	248,275	$	130.07

Summary of Restricted Stock Activity

		Weighted-Average
		Grant Date Fair
Unvested Service-Based Restricted Stock Units	Shares	Value
Unvested, beginning of period	783,219	$	123.04
Granted	227,989		134.60
Vested	(267,434)		118.11
Cancelled or expired	(9,329)		128.51
Unvested, end of period	734,445	$	128.42