Stock-based Compensation Plans (Summary of Stock Option Plan Activity) (Details) - $ / shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Shares
Outstanding, beginning of year, Shares	1,062,177	1,396,152	1,619,948
Granted, Shares	301,152	460,610	587,340
Exercised, Shares	(210,190)	(464,726)	(589,666)
Forfeited or cancelled, Shares	(54,063)	(329,859)	(221,470)
Outstanding, end of year, Shares	1,099,076	1,062,177	1,396,152
Additional Disclosures
Exercisable, end of year, Shares	515,286	423,883	441,256
Exercisable, end of year, Weighted Average Exercise Price	$ 69.83	$ 62.41	$ 53.59
Weighted Average Exercise Price
Outstanding, beginning of year, Weighted Average Exercise Price	75.53	68.63	56.57
Granted, Weighted Average Exercise Price	110.98	90.85	82.17
Exercised, Weighted Average Exercise Price	69.41	63.12	48.99
Forfeited or cancelled, Weighted Average Exercise Price	89.09	85.22	68.61
Outstanding, end of year, Weighted Average Exercise Price	$ 85.75	$ 75.53	$ 68.63