Condensed Consolidated Statements of Shareholders' Equity - USD ($) $ in Millions	Total		Common Stock [Member]	Additional Paid-In Capital [Member]	Treasury Shares [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) Member]
Beginning Balance at Dec. 31, 2018	$ 1,746.7		$ 45.3	$ 1,372.0	$ (455.1)	$ 862.6	$ (78.1)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	91.2					91.2
Other comprehensive income (loss) - change in fair value of fixed maturities, net of taxes	50.3						50.3
Other comprehensive income (loss) - other	0.2						0.2
Activity under stock incentive plans	4.2		0.1	4.1
Retirement of common shares (tax payments on equity compensation)	(1.6)		0.0	(1.6)
Employee stock purchase plan	0.4			0.4
Cash dividends declared - common shares	(10.8)					(10.8)
Ending Balance at Mar. 31, 2019	1,880.6		45.4	1,374.9	(455.1)	943.0	(27.6)
Beginning Balance at Dec. 31, 2019	1,781.1	[1]	45.7	1,376.6	(455.1)	811.1	2.8
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	(18.8)					(18.8)
Other comprehensive income (loss) - change in fair value of fixed maturities, net of taxes	(107.0)						(107.0)
Other comprehensive income (loss) - other	(3.4)						(3.4)
Activity under stock incentive plans	3.1		0.3	2.8
Retirement of common shares (tax payments on equity compensation)	(5.8)		(0.1)	(5.7)
Employee stock purchase plan	0.5			0.5
Cash dividends declared - common shares	(10.7)					(10.7)
Ending Balance at Mar. 31, 2020	$ 1,636.8		$ 45.9	$ 1,374.2	$ (455.1)	$ 773.7	$ (101.9)

[1] Derived from audited consolidated financial statements.