CONSOLIDATED STATEMENTS OF CHANGES IN SHAREHOLDERS' EQUITY (UNAUDITED) - USD ($) $ in Millions	Total	Common stock	Additional paid-in capital	Retained earnings	Accumulated other comprehensive income (loss), net of tax	Treasury stock, at cost
Beginning balance at Dec. 31, 2020		$ 0.1	$ 488.4	$ 1,434.6	$ 355.1	$ (488.1)
Increase (Decrease) in Stockholders' Equity
Options exercised and conversion of common stock units and restricted stock units			(1.2)
Share-based compensation expense			2.0
Net income	$ 39.3			39.3
Dividends, 2022, $0.32 per share; 2021, $0.31 per share				(13.1)
Change in net unrealized investment gains (losses) on fixed maturity securities					(122.7)
Acquisition of shares						(1.5)
Ending balance at Mar. 31, 2021	1,692.9	0.1	489.2	1,460.8	232.4	(489.6)
Beginning balance at Dec. 31, 2021	1,807.4	0.1	495.3	1,524.9	280.5	(493.4)
Increase (Decrease) in Stockholders' Equity
Options exercised and conversion of common stock units and restricted stock units			(0.6)
Share-based compensation expense			1.9
Net income	14.5			14.5
Dividends, 2022, $0.32 per share; 2021, $0.31 per share				(13.5)
Change in net unrealized investment gains (losses) on fixed maturity securities					(270.7)
Acquisition of shares						(2.2)
Ending balance at Mar. 31, 2022	$ 1,536.8	$ 0.1	$ 496.6	$ 1,525.9	$ 9.8	$ (495.6)