Stock-based Compensation Plans (Schedule of Stock Options by Exercise Price Range) (Details)	12 Months Ended
	Dec. 31, 2018 $ / shares shares
Share Based Compensation Shares Authorized Under Stock Option Plans Exercise Price Range [Line Items]
Exercise Price	$ 57.99
Options Outstanding, Number | shares	93,778
Options Outstanding, Weighted Average Remaining Contractual Lives	5 years 1 month 20 days
Options Outstanding, Weighted Average Exercise Price	$ 57.99
Options Currently Exercisable, Number | shares	93,778
Options Currently Exercisable, Weighted Average Exercise Price	$ 57.99
Exercise Price Range One [Member]
Share Based Compensation Shares Authorized Under Stock Option Plans Exercise Price Range [Line Items]
Range of Exercise Prices, Lower Range Limit	36.81
Range of Exercise Prices, Upper Range Limit	$ 46.47
Options Outstanding, Number | shares	64,367
Options Outstanding, Weighted Average Remaining Contractual Lives	3 years 5 months 8 days
Options Outstanding, Weighted Average Exercise Price	$ 41.61
Options Currently Exercisable, Number | shares	64,367
Options Currently Exercisable, Weighted Average Exercise Price	$ 41.61
Exercise Price Range Two [Member]
Share Based Compensation Shares Authorized Under Stock Option Plans Exercise Price Range [Line Items]
Range of Exercise Prices, Lower Range Limit	70.24
Range of Exercise Prices, Upper Range Limit	$ 72.66
Options Outstanding, Number | shares	165,924
Options Outstanding, Weighted Average Remaining Contractual Lives	6 years 1 month 28 days
Options Outstanding, Weighted Average Exercise Price	$ 70.27
Options Currently Exercisable, Number | shares	165,924
Options Currently Exercisable, Weighted Average Exercise Price	$ 70.27
Exercise Price Range Three [Member]
Share Based Compensation Shares Authorized Under Stock Option Plans Exercise Price Range [Line Items]
Range of Exercise Prices, Lower Range Limit	74.88
Range of Exercise Prices, Upper Range Limit	$ 82.74
Options Outstanding, Number | shares	190,120
Options Outstanding, Weighted Average Remaining Contractual Lives	7 years 3 months 18 days
Options Outstanding, Weighted Average Exercise Price	$ 80.75
Options Currently Exercisable, Number | shares	112,847
Options Currently Exercisable, Weighted Average Exercise Price	$ 80.49
Exercise Price Range Four [Member]
Share Based Compensation Shares Authorized Under Stock Option Plans Exercise Price Range [Line Items]
Range of Exercise Prices, Lower Range Limit	87.50
Range of Exercise Prices, Upper Range Limit	$ 91.19
Options Outstanding, Number | shares	285,280
Options Outstanding, Weighted Average Remaining Contractual Lives	8 years 2 months 12 days
Options Outstanding, Weighted Average Exercise Price	$ 90.66
Options Currently Exercisable, Number | shares	78,370
Options Currently Exercisable, Weighted Average Exercise Price	$ 90.89
Exercise Price Range Five [Member]
Share Based Compensation Shares Authorized Under Stock Option Plans Exercise Price Range [Line Items]
Range of Exercise Prices, Lower Range Limit	110.57
Range of Exercise Prices, Upper Range Limit	$ 124.14
Options Outstanding, Number | shares	299,607
Options Outstanding, Weighted Average Remaining Contractual Lives	9 years 2 months 4 days
Options Outstanding, Weighted Average Exercise Price	$ 110.98