Shareholders' Equity (Narrative) (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions		3 Months Ended	6 Months Ended
	Jul. 12, 2018	Jun. 30, 2018	Jun. 30, 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		Jun. 08, 2018
Dividend record date		Jun. 29, 2018
Dividends paid			$ 7.1
Dividend paid date		Jul. 12, 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		$ 237.6	$ 237.6
Subsequent Event [Member]
Dividends Payable [Line Items]
Dividends paid	$ 7.1
Accelerated Stock Repurchase Agreement [Member]
Equity Class Of Treasury Stock [Line Items]
Accelerated Share Repurchases Payment					$ (50.0)
Initial ASR share delivery					1.3
Accelerated Stock Repurchase Agreement [Member] | Subsequent Event [Member]
Equity Class Of Treasury Stock [Line Items]
Initial ASR share delivery				0.4