Stock Award Plans, Employee Plan Outstanding and Exercisable Options (Details) - Employee Stock Award Plan [Member] - Stock Options [Member]	12 Months Ended
	Dec. 31, 2017 USD ($) $ / shares shares
First Price Range [Member]
Outstanding and Exercisable Stock options [Abstract]
Range of Exercise Prices, lower limit (in dollars per share)	$ 46.74
Range of Exercise Prices, upper limit (in dollars per share)	$ 51.23
Options Outstanding [Abstract]
Number Outstanding (in shares) | shares	197,776
Weighted Average Remaining Contractual Life	3 years 9 months 18 days
Weighted Average Exercise Price, Options Outstanding (in dollars per share)	$ 50.02
Options Exercisable [Abstract]
Number Exercisable (in shares) | shares	100,806
Weighted Average Exercise Price, Options Exercisable (in dollars per share)	$ 48.86
Second Price Range [Member]
Outstanding and Exercisable Stock options [Abstract]
Range of Exercise Prices, lower limit (in dollars per share)	64.65
Range of Exercise Prices, upper limit (in dollars per share)	$ 74.99
Options Outstanding [Abstract]
Number Outstanding (in shares) | shares	394,704
Weighted Average Remaining Contractual Life	4 years
Weighted Average Exercise Price, Options Outstanding (in dollars per share)	$ 69.68
Options Exercisable [Abstract]
Number Exercisable (in shares) | shares	217,627
Weighted Average Exercise Price, Options Exercisable (in dollars per share)	$ 70.25
Third Price Range [Member]
Outstanding and Exercisable Stock options [Abstract]
Range of Exercise Prices, lower limit (in dollars per share)	93.64
Range of Exercise Prices, upper limit (in dollars per share)	$ 96.85
Options Outstanding [Abstract]
Number Outstanding (in shares) | shares	33,987
Weighted Average Remaining Contractual Life	3 years 1 month 6 days
Weighted Average Exercise Price, Options Outstanding (in dollars per share)	$ 94.31
Options Exercisable [Abstract]
Number Exercisable (in shares) | shares	33,987
Weighted Average Exercise Price, Options Exercisable (in dollars per share)	$ 94.31
Fourth Price Range [Member]
Outstanding and Exercisable Stock options [Abstract]
Range of Exercise Prices, lower limit (in dollars per share)	101.46
Range of Exercise Prices, upper limit (in dollars per share)	$ 104.37
Options Outstanding [Abstract]
Number Outstanding (in shares) | shares	28,188
Weighted Average Remaining Contractual Life	3 years 2 months 12 days
Weighted Average Exercise Price, Options Outstanding (in dollars per share)	$ 102.88
Options Exercisable [Abstract]
Number Exercisable (in shares) | shares	28,188
Weighted Average Exercise Price, Options Exercisable (in dollars per share)	$ 102.88
Full Exercise Price Range [Member]
Outstanding and Exercisable Stock options [Abstract]
Range of Exercise Prices, lower limit (in dollars per share)	46.74
Range of Exercise Prices, upper limit (in dollars per share)	$ 104.37
Options Outstanding [Abstract]
Number Outstanding (in shares) | shares	654,655
Weighted Average Remaining Contractual Life	3 years 9 months 18 days
Weighted Average Exercise Price, Options Outstanding (in dollars per share)	$ 66.45
Aggregate Intrinsic Value, Options Outstanding | $	$ 3,455,000
Options Exercisable [Abstract]
Number Exercisable (in shares) | shares	380,608
Weighted Average Exercise Price, Options Exercisable (in dollars per share)	$ 69.15
Aggregate Intrinsic Value, Options Exercisable | $	$ 1,883,000