Consolidated Statement of Changes in Stockholders' Equity - USD ($) $ in Millions	Total	Common stock	Retained earnings	Accumulated other comprehensive loss
Equity, beginning balance at Dec. 31, 2021	$ 1,986.6	$ 945.0	$ 1,052.6	$ (11.0)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	30.7	0.0	30.7	0.0
Other comprehensive income (loss), net of tax expense	$ (318.8)	0.0	0.0	(318.8)
Stock repurchased and retired (in shares)	1,759,742
Common shares issued (in shares)	46,913,370
Non-vested common shares issued (in shares)	453,439
Stock Issued During Period, Shares, Restricted Stock Award, Forfeited	67,292
Stock Issued During Period, Value, Stock Options Exercised	$ 0.1	0.1	0.0	0.0
Common stock transactions:
Common shares purchased and retired	(65.9)	(65.9)	0.0	0.0
Common shares issued	1,722.5	1,722.5	0.0	0.0
Non-vested common shares issued	0.0	0.0	0.0	0.0
Non-vested common shares forfeited or canceled	0.0	0.0	0.0	0.0
Stock-based compensation expense	$ 6.2	6.2	0.0	0.0
Common dividends (in dollars per share)	$ 0.82
Common cash dividend declared	$ (89.5)	0.0	(89.5)	0.0
Equity, ending balance at Jun. 30, 2022	3,271.9	2,607.9	993.8	(329.8)
Equity, beginning balance at Mar. 31, 2022	3,441.1	2,668.6	974.5	(202.0)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	64.1	0.0	64.1	0.0
Other comprehensive income (loss), net of tax expense	$ (127.8)	0.0	0.0	(127.8)
Stock repurchased and retired (in shares)	1,722,044
Common shares issued (in shares)	26,266
Non-vested common shares issued (in shares)	2,626
Stock Issued During Period, Shares, Restricted Stock Award, Forfeited	51,820
Common stock transactions:
Common shares purchased and retired	$ (64.5)	(64.5)	0.0	0.0
Common shares issued	0.0	0.0	0.0	0.0
Non-vested common shares issued	0.0	0.0	0.0	0.0
Non-vested common shares forfeited or canceled	0.0	0.0	0.0	0.0
Stock-based compensation expense	$ 3.8	3.8	0.0	0.0
Common dividends (in dollars per share)	$ 0.41
Common cash dividend declared	$ (44.8)	0.0	(44.8)	0.0
Equity, ending balance at Jun. 30, 2022	3,271.9	2,607.9	993.8	(329.8)
Equity, beginning balance at Dec. 31, 2022	3,073.8	2,478.2	1,072.7	(477.1)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	123.3	0.0	123.3	0.0
Other comprehensive income (loss), net of tax expense	$ 18.1	0.0	0.0	18.1
Stock repurchased and retired (in shares)	55,428
Common shares issued (in shares)	54,414
Non-vested common shares issued (in shares)	616,497
Stock Issued During Period, Shares, Restricted Stock Award, Forfeited	36,823
Common stock transactions:
Common shares purchased and retired	$ (1.8)	(1.8)	0.0	0.0
Common shares issued	0.0	0.0	0.0	0.0
Non-vested common shares issued	0.0	0.0	0.0	0.0
Non-vested common shares forfeited or canceled	0.0	0.0	0.0	0.0
Stock-based compensation expense	$ 5.0	5.0	0.0	0.0
Common dividends (in dollars per share)	$ 0.94
Common cash dividend declared	$ (97.2)	0.0	(97.2)	0.0
Equity, ending balance at Jun. 30, 2023	3,121.2	2,481.4	1,098.8	(459.0)
Equity, beginning balance at Mar. 31, 2023	3,160.3	2,478.7	1,080.7	(399.1)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	67.0	0.0	67.0	0.0
Other comprehensive income (loss), net of tax expense	$ (59.9)	0.0	0.0	(59.9)
Stock repurchased and retired (in shares)	348
Common shares issued (in shares)	54,414
Non-vested common shares issued (in shares)	605,634
Stock Issued During Period, Shares, Restricted Stock Award, Forfeited	21,035
Common stock transactions:
Common shares purchased and retired	$ 0.0	0.0	0.0	0.0
Common shares issued	0.0	0.0	0.0	0.0
Non-vested common shares issued	0.0	0.0	0.0	0.0
Non-vested common shares forfeited or canceled	0.0	0.0	0.0	0.0
Stock-based compensation expense	$ 2.7	2.7	0.0	0.0
Common dividends (in dollars per share)	$ 0.47
Common cash dividend declared	$ (48.9)	0.0	(48.9)	0.0
Equity, ending balance at Jun. 30, 2023	$ 3,121.2	$ 2,481.4	$ 1,098.8	$ (459.0)