Consolidated Statements of Shareholders' Equity - USD ($) $ in Millions	Total	Common Shares [Member]	Additional Paid-In Capital [Member]	Treasury Shares [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]
Beginning Balance at Dec. 31, 2015	$ 1,668.1	$ 37.1	$ 964.9	$ (331.1)	$ 985.7	$ 11.5
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	146.7				146.7
Other comprehensive income (loss), net of tax	36.2					36.2
Repurchase of common shares	(47.1)			(47.1)
Activity under stock incentive plans	15.4	0.2	15.2
Retirement of common shares (tax payments on equity compensation)	(2.1)		(2.1)
Deferred tax - share-based payments	0.7		0.7
Employee stock purchase plan	1.4		1.4
Stock Dividend		2.7	143.2		(145.9)
Cash dividend declared - common shares	(26.6)				(26.6)
Ending Balance at Dec. 31, 2016	1,792.7	40.0	1,123.3	(378.2)	959.9	47.7
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	50.3				50.3
Other comprehensive income (loss), net of tax	48.9					48.9
Repurchase of common shares	(45.2)			(45.2)
Activity under stock incentive plans	12.4	0.4	12.0
Retirement of common shares (tax payments on equity compensation)	(8.2)	(0.1)	(8.1)
Employee stock purchase plan	2.0	0.1	1.9
Cash dividend declared - common shares	(33.2)				(33.2)
Ending Balance at Dec. 31, 2017	1,819.7	40.4	1,129.1	(423.4)	977.0	96.6
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect of adoption of ASU, net of taxes | Accounting Standards Update 2016-01 [Member]					117.5	(117.5)
Cumulative effect of adoption of ASU, net of taxes | Accounting Standards Update 2018-02 [Member]					(20.7)	20.7
Net income	63.6				63.6
Other comprehensive income (loss), net of tax	(77.9)					(77.9)
Repurchase of common shares	(31.7)			(31.7)
Activity under stock incentive plans	15.9	0.6	15.3
Retirement of common shares (tax payments on equity compensation)	(7.4)	(0.1)	(7.3)
Employee stock purchase plan	2.0		2.0
Stock Dividend		4.4	232.9		(237.3)
Cash dividend declared - common shares	(37.5)				(37.5)
Ending Balance at Dec. 31, 2018	$ 1,746.7	$ 45.3	$ 1,372.0	$ (455.1)	$ 862.6	$ (78.1)