Investments (Tables)

12 Months Ended

Dec. 31, 2024

Investments, Debt and Equity Securities [Abstract]

Amortized cost and fair values

The following tables present cost or amortized cost and fair values of investments in fixed maturities at December 31, 2024 and 2023, respectively ($ in millions):

	Cost or Amortized Cost		Gross Unrealized				Fair Value
			Gains		Losses
December 31, 2024
Corporate debt securities	$	470.6	$	1.3	$	(1.1)	$	470.8
U.S. Government obligations	107.6		0.3		(0.2)		107.7
Asset-backed securities	22.9		—		—		22.9
Non-U.S. government obligations	6.0		—		—		6.0
Total	$	607.1	$	1.6	$	(1.3)	$	607.4
December 31, 2023
Corporate debt securities	$	453.6	$	1.3	$	(5.0)	$	449.9
U.S. Government obligations	176.8		0.4		(1.3)		175.9
Asset-backed securities	1.6		—		—		1.6
Non-U.S. government obligations	—		—		—		—
Total	$	632.0	$	1.7	$	(6.3)	$	627.4

Contractual maturities of bonds

The following table presents the cost or amortized cost and estimated fair value of investments in fixed maturities as of December 31, 2024 by contractual maturity ($ in millions). Expected maturities may differ from contractual maturities because borrowers may have the right to call or prepay obligations with or without call or prepayment penalties.

	December 31, 2024
	Cost or Amortized Cost		Fair Value
Due in one year or less	$	233.1	$	233.1
Due after one year through five years	373.8		374.1
Due after five years through ten years	0.2		0.2
Due after ten years	—		—
Total	$	607.1	$	607.4

Aging of gross unrealized losses

The following tables present the gross unrealized losses and related fair values for the Company's investment in fixed maturities, grouped by duration of time in a continuous unrealized loss position as of December 31, 2024 and 2023 ($ in millions):

	Less than 12 Months				12 Months or More				Total
	Fair Value		Gross Unrealized Losses		Fair Value		Gross Unrealized Losses		Fair Value		Gross Unrealized Losses
December 31, 2024
Corporate debt securities	$	149.4	$	(0.6)	$	53.0	$	(0.5)	$	202.4	$	(1.1)
U.S. Government obligations	27.6		(0.2)		—		—		27.6		(0.2)
Asset-backed securities	5.8		—		—		—		5.8		—
Non-U.S. government obligations	—		—		—		—		—		—
Total	$	182.8	$	(0.8)	$	53.0	$	(0.5)	$	235.8	$	(1.3)
December 31, 2023
Corporate debt securities	$	89.0	$	(1.2)	$	178.3	$	(4.0)	$	267.3	$	(5.2)
U.S. Government obligations	79.6		(0.2)		57.7		(0.9)		137.3		(1.1)
Asset-backed securities	—		—		0.2		—		0.2		—
Non-U.S. government obligations	—		—		—		—		—		—
Total	$	168.6	$	(1.4)	$	236.2	$	(4.9)	$	404.8	$	(6.3)

Net investment income

An analysis of net investment income follows ($ in millions):

	December 31,
	2024		2023		2022
Interest on cash and cash equivalents	$	8.3	$	4.2	$	1.2
Fixed maturities	24.4		17.0		5.7
Short-term investments	1.6		3.8		1.9
Total	34.3		25.0		8.8
Investment expense	0.3		0.3		0.4
Net investment income	$	34.0	$	24.7	$	8.4

Special deposits

The carrying value of bonds deposited with each respective state is as follows ($ in millions):

	December 31,
U.S. State	2024		2023
Delaware	$	2.8	$	2.8
New York	2.6		2.9
Washington	1.2		1.2
Colorado	1.1		1.1
Virginia	0.9		0.8
New Mexico	0.7		0.7
New Jersey	0.6		0.6
North Carolina	0.6		0.6
Nevada	0.4		0.2
Ohio	0.4		—
Arkansas	0.3		0.1
Florida	0.2		0.2
Massachusetts	0.2		0.2
Kansas	0.1		0.2
Kentucky	0.1		0.1
Total	$	12.2	$	11.7