Stock-based compensation

3 Months Ended

Mar. 31, 2021

Share-based Payment Arrangement [Abstract]

11. Stock-based compensation

The following table presents the components of stock-based compensation expense:


(in millions)	Classification	Three months ended March 31,
		2021		2020
Stock options	Equity	$	4.6	$	3.9
RSUs	Equity	5.7		4.9
Optionholder awards	Liability	—		0.3
Other	Both	1.1		(0.7)
Total		$	11.4	$	8.4
Balance sheet classification:
Equity		$	10.8	$	9.2
Liability		0.6		(0.8)

At March 31, 2021, unvested awards under our plans have remaining stock-based compensation expense of $114.8 million to be recognized over a weighted average period of 1.9 years.

At March 31, 2021, 9.8 million shares were available for future issuance under the 2019 Plan.

Stock options

The following table presents information about outstanding stock options:


(options and intrinsic value in millions)	Number of options	Weighted average exercise price per option		Aggregate intrinsic value		Weighted average remaining term
Balance at December 31, 2020	20.0	$	18.80
Granted	1.5	27.70
Exercised	(1.0)	21.40
Forfeited	(0.1)	15.88
Balance at March 31, 2021	20.4	19.32		$	197.0	7.5 years
Expected to vest	9.0	19.80		83.2		8.6 years
Vested	11.4	18.93		113.7		6.6 years

During the three months ended March 31, 2021, we granted stock options that have a contractual life of ten years and will vest annually over four years, subject to the recipient continuously providing service to us through each such date.

RSUs

The following table presents information about unvested RSUs:


(awards in millions)	Number of awards	Weighted average grant date fair value per award
Balance at December 31, 2020	4.9	$	15.31
Granted	1.1	29.17
Vested	(0.7)	15.38
Forfeited	—	18.51
Balance at March 31, 2021	5.3	18.73

During the three months ended March 31, 2021, we granted RSUs that will vest annually over four years, subject to the recipient continuously providing service to us through each such date. Additionally, we granted certain employees RSUs that cliff vest over three years and contain performance and market conditions that impact the number of shares that will ultimately vest, subject to the recipient continuously providing service to us through each such date. The expense recorded related to the RSUs with performance and market conditions was not material.