Earnings Per Share (Narrative) (Details) - shares shares in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Earnings Per Share [Abstract]
Basic weighted average number of common shares outstanding for all classes of common shares (in shares)	49.5	47.8	49.4	47.6
Antidilutive securities excluded from computation of diluted net earnings per share (in shares)	0.7	0.7	0.8	2.3