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Shareholders' Equity (Narrative) (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions		3 Months Ended	9 Months Ended
	Oct. 11, 2018	Sep. 30, 2018	Sep. 30, 2018	Oct. 26, 2018	Jul. 18, 2018	Mar. 09, 2018	Mar. 06, 2018	Dec. 07, 2015
Dividends Payable [Line Items]
Quarterly cash dividend declared		$ 0.15
Dividend declared date		Sep. 17, 2018
Dividend record date		Sep. 28, 2018
Dividends paid			$ 14.2
Dividend paid date		Oct. 11, 2018
Equity Class Of Treasury Stock [Line Items]
Repurchase of common shares program authorized amount							$ 250.0	$ 100.0
Repurchase of common shares remaining authorized amount		$ 191.4	$ 191.4
Subsequent Event [Member]
Dividends Payable [Line Items]
Dividends paid	$ 6.8
Equity Class Of Treasury Stock [Line Items]
Repurchase of common shares program authorized amount				$ 100.0
Accelerated Stock Repurchase Agreement [Member]
Equity Class Of Treasury Stock [Line Items]
Accelerated Share Repurchases Payment						$ (50.0)
ASR share delivery					0.4	1.3