Marketable Securities and Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2021

Fair Value Disclosures [Abstract]

Summary of assets measured at fair value on a recurring basis

The following is a summary of the Company’s assets measured at fair value on a recurring basis.

	December 31, 2021
(dollars in millions)	Valuation Hierarchy	Effective Maturity	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Fair Value
Corporate bonds	Level 2	2022	$	784.0	$	0.0	$	(0.7)	$	783.3
Corporate bonds	Level 2	2023 - 2024	582.6		—		(3.9)		578.7
Government securities	Level 2	2022	32.4		—		(0.1)		32.3
Total			$	1,399.0	$	0.0	$	(4.7)	$	1,394.3

	December 31, 2020
(dollars in millions)	Valuation Hierarchy	Effective Maturity	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Fair Value
Corporate bonds	Level 2	2021	$	99.6	$	0.6	$	—	$	100.2
Total			$	99.6	$	0.6	$	—	$	100.2