Stock Incentive Plans (Details 2) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Options Granted
Employee Service Share-based Compensation, Tax Benefit from Exercise of Stock Options	$ 2.2	$ 7.4	$ 11.2
Options, additional information
Total unrecognized stock-based compensation expense	$ 1.8
Weighted-average period over which this expense will be recognized	9 months 18 days
Minimum
Options, additional information
Performance Based Compensation Payout Target	0.00%
Maximum
Options, additional information
Performance Based Compensation Payout Target	200.00%
Employee nonstatutory stock options
Stock Incentive Plans
Number Outstanding (in shares)	1,873,795
Number Exercisable (in shares)	1,209,432
Weighted-average remaining contractual term of exercisable options (in years)	2 years 1 month 9 days
Options Granted
Options granted (in shares)	428,190	316,830	377,920
Stock or Unit Option Plan Expense	$ 5.8	$ 4.3	$ 6.0
Assumptions used for estimating the fair value of stock options
Weighted average expected volatility (as a percent)	23.70%	24.80%	26.60%
Risk-free rate	2.55%	1.66%	1.01%
Dividend yield	1.40%	1.20%	1.00%
Volatility rate, minimum	22.90%	23.80%	26.20%
Volatility rate, maximum	24.40%	25.10%	27.50%
Options, additional information
Stock or Unit Option Plan Expense	$ 5.8	$ 4.3	$ 6.0
Employee nonstatutory stock options | Minimum
Assumptions used for estimating the fair value of stock options
Expected term	3 years	3 years	3 years
Employee nonstatutory stock options | Maximum
Assumptions used for estimating the fair value of stock options
Expected term	6 years 6 months	4 years	4 years
Employee nonstatutory stock options | Exercise Price Range One [Member]
Stock Incentive Plans
Exercise price, low	$ 0
Exercise price, high	10
Employee nonstatutory stock options | Exercise Price Range Two [Member]
Stock Incentive Plans
Exercise price, low	10
Exercise price, high	20
Employee nonstatutory stock options | Exercise Price Range Three [Member]
Stock Incentive Plans
Exercise price, low	20
Exercise price, high	30
Employee nonstatutory stock options | Exercise Price Range Four [Member]
Stock Incentive Plans
Exercise price, low	30
Exercise price, high	40
Employee nonstatutory stock options | Exercise Price Range Five [Member]
Stock Incentive Plans
Exercise price, low	40
Exercise price, high	50
Employee nonstatutory stock options | Exercise Price Range Six [Member]
Stock Incentive Plans
Exercise price, low	50
Exercise price, high	60
Employee nonstatutory stock options | Exercise Price Range Seven [Member]
Stock Incentive Plans
Exercise price, low	60
Exercise price, high	$ 70
Number Outstanding (in shares)	710,321
Number Exercisable (in shares)	226,938
Outstanding Weighted- Average Remaining Contractual Life (Years)	3 years 2 months 23 days
Weighted-Average Exercise Price (in dollars per share)	$ 68.27
Employee nonstatutory stock options | Exercise Price Range Eight [Member]
Stock Incentive Plans
Exercise price, low	70
Exercise price, high	$ 80
Number Outstanding (in shares)	1,139,369
Number Exercisable (in shares)	958,389
Outstanding Weighted- Average Remaining Contractual Life (Years)	1 year 5 months 16 days
Weighted-Average Exercise Price (in dollars per share)	$ 75.72
Employee nonstatutory stock options | Exercise Price Range Nine [Member]
Stock Incentive Plans
Exercise price, low	80
Exercise price, high	$ 90
Number Outstanding (in shares)	24,105
Number Exercisable (in shares)	24,105
Outstanding Weighted- Average Remaining Contractual Life (Years)	1 month 27 days
Weighted-Average Exercise Price (in dollars per share)	$ 80.76
Employee nonstatutory stock options | Exercise Price Range Ten [Member]
Stock Incentive Plans
Exercise price, low	90
Exercise price, high	100
Employee nonstatutory stock options | Exercise Price Range Eleven [Member]
Stock Incentive Plans
Exercise price, low	100
Exercise price, high	$ 110
Restricted Stock Units (RSUs) [Member]
Options, additional information
Performance Based Units Granted	86,698	57,600	77,358
Granted (in dollars per share)	$ 67.54	$ 71.37	$ 68.90
Performance Based Units [Member]
Options, additional information
Performance Based Units Granted	93,216	115,158	124,952
Granted (in dollars per share)	$ 67.39	$ 71.37	$ 68.50
Restricted Stock Units (RSUs) and Performance Stock Units (PSUs) [Member]
Options Granted
Stock or Unit Option Plan Expense	$ 13.2	$ 10.3	$ 8.6
Options, additional information
Performance Based Units, Forfeitures	44,279	16,395	15,197
Percent of Units Expected to Settle in Common Stock	64.00%	65.00%	67.00%
Percent of Units Expected to Settle in Cash	36.00%	35.00%	33.00%
Stock or Unit Option Plan Expense	$ 13.2	$ 10.3	$ 8.6
Stock or Unit Option Plan Expense, Unrecognized	$ 9.5
Weighted-Average Remaining Contractual Term (in years)	1 year 6 months