Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Numerator:
Income from continuing operations	$ 68.5	$ 39.5
Less: dividends declared - common stock outstanding, restricted shares and restricted share units	(19.5)	(16.7)
Undistributed earnings	$ 49.0	$ 22.8
Percent allocated to common shareholders	99.30%	99.50%
Undistributed earnings allocated to common shareholders	$ 48.6	$ 22.7
Add: dividends declared - common stock	19.2	16.2
Numerator for basic and diluted EPS	$ 67.8	$ 38.9
Denominator (in thousands):
Denominator for basic EPS: weighted-average common shares outstanding	64,018	64,876
Effect of dilutive securities:
Performance awards (in shares)	325	220
Stock options (in shares)	533	800
Denominator for diluted EPS: adjusted weighted-average common shares outstanding and assumed conversion	64,876	65,896
Per share income from continuing operations:
Basic (in dollars per share)	$ 1.06	$ 0.60
Diluted (in dollars per share)	$ 1.05	$ 0.59
Basic weighted-average common shares outstanding	64,018	64,876
Basic weighted-average common shares outstanding, unvested restricted shares expected to vest and restricted share units	64,491	65,210
Percent allocated to common shareholders	99.30%	99.50%
Income (loss) from discontinued operations and net income
Income (loss) from discontinued operations attributable to common shareholders for basic and diluted earnings per share		$ (0.1)
Net income attributable to common shareholders for basic and diluted earnings per share	$ 67.8	$ 38.8
Antidilutive stock options excluded from EPS calculation (in shares)	544