Shareholders' Equity - RSU Awards and SSAR Awards (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
RSUs
Awards Outstanding
Balance at the beginning of the period (in shares)	700,000	800,000	700,000
Granted (in shares)	700,000	200,000	300,000
Issued (in shares)		(300,000)	(200,000)
Vested (in shares)	(100,000)
Forfeited (in shares)	(100,000)	0	0
Balance at the end of the period (in shares)	1,200,000	700,000	800,000	700,000
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Balance at the beginning of the period (in dollars per share)	$ 43.10	$ 38.55	$ 35.61
Granted (in dollars per share)	44.23	51.00	44.34
Issued (in dollars per share)		38.80	36.67
Vested (in dollars per share)	42.78
Forfeited (in dollars per share)	44.78	42.65	40.25
Balance at the end of the period (in dollars per share)	$ 43.28	$ 43.10	$ 38.55	$ 35.61
Aggregate Intrinsic Value	$ 55.7	$ 28.0	$ 36.9	$ 31.8
Weighted Average Remaining Vesting Term	1 year 6 months 29 days	1 year 8 months 28 days	1 year 5 months 22 days	1 year 4 months 1 day
Aggregate intrinsic value of awards issued	$ 6.2	$ 15.3	$ 10.1
SSAR Awards
Awards Outstanding
Balance at the beginning of the period (in shares)	200,000	200,000	200,000
Granted (in shares)	100,000	0
Exercised (in shares)	0	0	0
Forfeited (in shares)			0
Balance at the end of the period (in shares)	300,000	200,000	200,000	200,000
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Balance at the beginning of the period (in dollars per share)	$ 42.91	$ 40.06	$ 37.69
Granted (in dollars per share)	48.58
Exercised (in dollars per share)	40.91	57.48	22.26
Forfeited (in dollars per share)		25.08	40.91
Balance at the end of the period (in dollars per share)	$ 44.97	$ 42.91	$ 40.06	$ 37.69
Aggregate Intrinsic Value	$ 0.3	$ 0.0	$ 1.5	$ 1.5
Weighted Average Remaining Vesting Term	2 years 4 months 20 days	2 years 5 months 16 days	3 years 15 days	3 years 7 months 5 days
SSAR Awards Exercisable
SSAR Awards (in shares)	200,000	0	0	0
Weighted Average Exercise Price (in dollars per share)	$ 42.15	$ 42.06	$ 35.81	$ 23.25
Aggregate Intrinsic Value	$ 0.7	$ 0.0	$ 0.6	$ 1.1
Weighted Average Remaining Contractual Life	1 year 4 months 4 days	2 years 2 months 14 days	2 years 2 months 10 days	11 months 20 days
Aggregate intrinsic value of SSAR Awards exercised	$ 0.1	$ 0.5	$ 0.8
Assumptions used to determine weighted average fair value
Weighted average fair value of SSAR Awards (in dollars per share)	$ 12.32	$ 14.78
Expected term	4 years 6 months	4 years 3 months 18 days
Volatility	29.80%	30.20%
Dividend yields	0.50%	0.30%
Risk-free interest rates	1.20%	1.20%
Shares issued in period (in shares)			0