Investments (Tables)

3 Months Ended

Mar. 31, 2025

Investments, Debt and Equity Securities [Abstract]

Amortized cost and fair values

The following tables present cost or amortized cost and fair values of investment in fixed maturities as of March 31, 2025 and December 31, 2024 ($ in millions):

	Cost or Amortized Cost		Gross Unrealized				Fair Value
			Gains		Losses
March 31, 2025
Corporate debt securities	$	519.3	$	1.7	$	(0.5)	$	520.5
U.S. Government obligations	100.3		0.4		(0.1)		100.6
Asset-backed securities	27.0		—		—		27.0
Non-U.S. government obligations	7.5		—		—		7.5
Total	$	654.1	$	2.1	$	(0.6)	$	655.6
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

Contractual maturities of bonds

The following table presents the cost or amortized cost and estimated fair value of investments in fixed maturities as of March 31, 2025 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.

	March 31, 2025
	Cost or Amortized Cost		Fair Value
Due in one year or less	$	309.7	$	310.1
Due after one year through five years	344.2		345.3
Due after five years through ten years	0.2		0.2
Due after ten years	—		—
Total	$	654.1	$	655.6

Net investment income

Details of the Company's net investment income is as follows ($ in millions):

	Three Months Ended March 31,
	2025		2024
Interest on cash and cash equivalents	$	2.2	$	1.5
Fixed maturities	7.1		5.8
Short-term investments	0.3		0.4
Total	9.6		7.7
Investment expense	0.1		0.1
Net investment income	$	9.5	$	7.6

Aging of gross unrealized losses

The following table presents 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 March 31, 2025 and December 31, 2024 ($ 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
March 31, 2025
Corporate debt securities	$	85.0	$	(0.2)	$	43.7	$	(0.3)	$	128.7	$	(0.5)
U.S. Government obligations	12.1		(0.1)		—		—		12.1		(0.1)
Asset-backed securities	9.3		—		—		—		9.3		—
Non-US government obligations	—		—		—		—		—		—
Total	$	106.4	$	(0.3)	$	43.7	$	(0.3)	$	150.1	$	(0.6)

	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-US government obligations	—		—		—		—		—		—
Total	$	182.8	$	(0.8)	$	53.0	$	(0.5)	$	235.8	$	(1.3)