Condensed Consolidated Statements of Shareholders' Equity - USD ($) $ in Millions	Total	Preferred Shares and Additional Paid-in Capital	Common Shares	Additional Paid-In Capital	Treasury Shares	Retained Earnings	Accumulated Other Comprehensive Income (Loss)
Beginning Balance at Dec. 31, 2021	$ 1,735.2	$ 144.0	$ 46.2	$ 1,386.4	$ (455.1)	$ 636.4	$ (22.7)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	(17.2)					(17.2)
Other comprehensive loss - Change in fair value of fixed maturities, net of taxes	(264.7)						(264.7)
Other comprehensive income, net - Other	31.4						31.4
Activity under stock incentive plans	3.0		0.1	2.9
Retirement of common shares (tax payments on equity compensation)	(1.3)			(1.3)
Employee stock purchase plan	0.9			0.9
Dividends on preferred shares	(5.3)					(5.3)
Cash dividend declared - common shares	(21.3)					(21.3)
Ending Balance at Jun. 30, 2022	1,460.7	144.0	46.3	1,388.9	(455.1)	592.6	(256.0)
Beginning Balance at Mar. 31, 2022	1,610.8	144.0	46.3	1,388.5	(455.1)	622.0	(134.9)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	(16.2)					(16.2)
Other comprehensive loss - Change in fair value of fixed maturities, net of taxes	(121.1)						(121.1)
Activity under stock incentive plans	0.2			0.2
Retirement of common shares (tax payments on equity compensation)	(0.3)			(0.3)
Employee stock purchase plan	0.5			0.5
Dividends on preferred shares	(2.7)					(2.7)
Cash dividend declared - common shares	(10.5)					(10.5)
Ending Balance at Jun. 30, 2022	1,460.7	144.0	46.3	1,388.9	(455.1)	592.6	(256.0)
Beginning Balance at Dec. 31, 2022	1,232.9	144.0	46.4	1,395.4	(455.1)	407.3	(305.1)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	(31.6)					(31.6)
Other comprehensive loss - Change in fair value of fixed maturities, net of taxes	37.5						37.5
Other comprehensive income, net - Other	1.3						1.3
Activity under stock incentive plans	(0.2)		0.1	(0.3)
Retirement of common shares (tax payments on equity compensation)	(0.8)			(0.8)
Employee stock purchase plan	0.8			0.8
Dividends on preferred shares	(5.3)					(5.3)
Cash dividend declared - common shares	0.2					0.2
Ending Balance at Jun. 30, 2023	1,234.8	144.0	46.5	1,395.1	(455.1)	370.6	(266.3)
Beginning Balance at Mar. 31, 2023	1,244.5	144.0	46.5	1,396.6	(455.1)	370.9	(258.4)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	2.2					2.2
Other comprehensive loss - Change in fair value of fixed maturities, net of taxes	(8.0)						(8.0)
Other comprehensive income, net - Other	0.1						0.1
Activity under stock incentive plans	(1.9)			(1.9)
Employee stock purchase plan	0.4			0.4
Dividends on preferred shares	(2.7)					(2.7)
Cash dividend declared - common shares	0.2					0.2
Ending Balance at Jun. 30, 2023	$ 1,234.8	$ 144.0	$ 46.5	$ 1,395.1	$ (455.1)	$ 370.6	$ (266.3)