Stock Award Plans, Director Plan Outstanding and Exercisable Options (Details) - Director Plan [Member] - Stock Options [Member]	12 Months Ended
	Dec. 31, 2018 USD ($) $ / shares shares
First Price Range [Member]
Outstanding and Exercisable Stock options [Abstract]
Range of Exercise Prices, upper limit (in dollars per share)	$ 29.60
Options Outstanding [Abstract]
Number Outstanding (in shares) | shares	6,000
Weighted Average Remaining Contractual Life	3 months 18 days
Weighted Average Exercise Price, Options Outstanding (in dollars per share)	$ 29.6
Options Exercisable [Abstract]
Number Exercisable (in shares) | shares	6,000
Weighted Average Exercise Price, Options Exercisable (in dollars per share)	$ 29.60
Second Price Range [Member]
Outstanding and Exercisable Stock options [Abstract]
Range of Exercise Prices, lower limit (in dollars per share)	41.24
Range of Exercise Prices, upper limit (in dollars per share)	$ 56.45
Options Outstanding [Abstract]
Number Outstanding (in shares) | shares	31,276
Weighted Average Remaining Contractual Life	1 year 10 months 24 days
Weighted Average Exercise Price, Options Outstanding (in dollars per share)	$ 50.61
Options Exercisable [Abstract]
Number Exercisable (in shares) | shares	31,276
Weighted Average Exercise Price, Options Exercisable (in dollars per share)	$ 50.61
Third Price Range [Member]
Outstanding and Exercisable Stock options [Abstract]
Range of Exercise Prices, lower limit (in dollars per share)	61.89
Range of Exercise Prices, upper limit (in dollars per share)	$ 62.48
Options Outstanding [Abstract]
Number Outstanding (in shares) | shares	28,000
Weighted Average Remaining Contractual Life	3 years 7 months 6 days
Weighted Average Exercise Price, Options Outstanding (in dollars per share)	$ 62.27
Options Exercisable [Abstract]
Number Exercisable (in shares) | shares	28,000
Weighted Average Exercise Price, Options Exercisable (in dollars per share)	$ 62.27
Fourth Price Range [Member]
Outstanding and Exercisable Stock options [Abstract]
Range of Exercise Prices, lower limit (in dollars per share)	70.65
Range of Exercise Prices, upper limit (in dollars per share)	$ 99.52
Options Outstanding [Abstract]
Number Outstanding (in shares) | shares	65,828
Weighted Average Remaining Contractual Life	5 years 2 months 12 days
Weighted Average Exercise Price, Options Outstanding (in dollars per share)	$ 86.45
Options Exercisable [Abstract]
Number Exercisable (in shares) | shares	65,168
Weighted Average Exercise Price, Options Exercisable (in dollars per share)	$ 86.47
Full Exercise Price Range [Member]
Outstanding and Exercisable Stock options [Abstract]
Range of Exercise Prices, lower limit (in dollars per share)	29.60
Range of Exercise Prices, upper limit (in dollars per share)	$ 99.52
Options Outstanding [Abstract]
Number Outstanding (in shares) | shares	131,104
Weighted Average Remaining Contractual Life	3 years 9 months 18 days
Weighted Average Exercise Price, Options Outstanding (in dollars per share)	$ 70.14
Aggregate Intrinsic Value, Options Outstanding | $	$ 893,000
Options Exercisable [Abstract]
Number Exercisable (in shares) | shares	130,444
Weighted Average Exercise Price, Options Exercisable (in dollars per share)	$ 70.06
Aggregate Intrinsic Value, Options Exercisable | $	$ 893,000