Marketable Securities (Tables)

9 Months Ended

Sep. 30, 2023

Investments, Debt and Equity Securities [Abstract]

Schedule of Carrying Values of Marketable Securities

The carrying values of marketable securities and the balance sheet location at September 30, 2023 and December 31, 2022 consisted of the following:


	September 30, 2023
(Millions of dollars)	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses	Estimated Fair Value
Available-for-sale securities:

Marketable securities current
U.S. Government bonds	$	5.9	$	—	—	$	5.9
U.S. Corporate bonds	2.5		—		—	2.5

Investment income receivable	0.1		—		—	0.1
	8.5		—		—	8.5


	September 30, 2023
(Millions of dollars)	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Estimated Fair Value
Marketable securities non-current
U.S. Corporate bonds	5.9		—		—		5.9
Non U.S. Corporate bonds	1.5		—		—		1.5
	7.4		—		—		7.4

Total marketable securities	$	15.9	$	—	$	—	$	15.9


	December 31, 2022
(Millions of dollars)	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Estimated Fair Value
Available-for-sale securities:

Marketable securities current
U.S. Government bonds	$	8.8	$	—	$	—	$	8.8
U.S. Corporate bonds	6.0		—		—		6.0
Non U.S. Corporate bonds	3.0		—		—		3.0
Investment income receivable	0.1		—		—		0.1
	17.9		—		—		17.9

Marketable securities non-current
U.S. Corporate bonds	4.4		—		—		4.4



Total marketable securities	$	22.3	$	—	$	—	$	22.3

Schedule of Amortized Cost Basis and Fair Value of Available-for-Sale Marketable Securities

The amortized cost basis and fair value of the Company's available-for-sale marketable securities at September 30, 2023, by contractual maturity, are as follows:


(Millions of dollars)	Amortized Cost		Fair Value
Less than 1 year	$	15.8	$	15.8
1 to 2 years	—		—

Total	$	15.8	$	15.8