SHORT-TERM INVESTMENTS: (Tables)

12 Months Ended

Dec. 31, 2023

SHORT-TERM INVESTMENTS:

Schedule of short-term investments

Short-term investments were as follows ($ in millions):

	At December 31,
	2023			2022
Trading securities	$	599.1		$	208.0
Weighted average interest rate		5.7	%		4.5	%
Available-for-sale	$	0.2		$	0.3
Weighted average interest rate		0.8	%		0.8	%
Total	$	599.3		$	208.3

Summary of activity investments

The following table summarizes the activity of these investments by category (in millions):

	Years ended
	December 31,
	2023		2022
Trading:
Interest earned	$	21.0	$	4.4
Unrealized gain (loss) at the end of the period	$	(*)	$	(*)
Available-for-sale:
Interest earned	$	(*)	$	(*)
Investment redeemed	$	0.1	$	0.1

(*)   Less than $0.1 million

Schedule of contractual maturities of the Company's available-for-sale debt securities

At December 31, 2023 and 2022, contractual maturities of the available-for-sale debt securities are as follows (in millions):

	2023		2022
One year or less	$	—	$	—
Maturing after one year through five years		—		—
Maturing after five years through ten years		—		—
Due after 10 years		0.2		0.3
Total debt securities	$	0.2	$	0.3