Stock Plans and Stock Based Compensation - Options and SARs Outstanding and Exercisable (Details)	12 Months Ended
	Dec. 31, 2018 $ / shares shares
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Outstanding (in shares) | shares	225,375
Weighted average remaining contractual life (in years)	4 years 6 months 23 days
Weighted average exercise price (in dollars per share)	$ 48.02
Number exercisable (in shares) | shares	139,483
Weighted average exercise price (in dollars per share)	$ 44.06
$35.71-37.50
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Range of exercise prices, lower range (in dollars per share)	35.71
Range of exercise prices, upper range (in dollars per share)	$ 37.5
Outstanding (in shares) | shares	42,598
Weighted average remaining contractual life (in years)	2 years 7 months 12 days
Weighted average exercise price (in dollars per share)	$ 37.00
Number exercisable (in shares) | shares	42,598
Weighted average exercise price (in dollars per share)	$ 37.00
$37.51-41.00
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Range of exercise prices, lower range (in dollars per share)	37.51
Range of exercise prices, upper range (in dollars per share)	$ 41
Outstanding (in shares) | shares	33,623
Weighted average remaining contractual life (in years)	4 years 3 months 9 days
Weighted average exercise price (in dollars per share)	$ 40.60
Number exercisable (in shares) | shares	19,444
Weighted average exercise price (in dollars per share)	$ 40.60
$41.01-50.00
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Range of exercise prices, lower range (in dollars per share)	41.01
Range of exercise prices, upper range (in dollars per share)	$ 50
Outstanding (in shares) | shares	90,478
Weighted average remaining contractual life (in years)	3 years 11 months 6 days
Weighted average exercise price (in dollars per share)	$ 46.43
Number exercisable (in shares) | shares	59,900
Weighted average exercise price (in dollars per share)	$ 45.01
$50.01-76.90
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Range of exercise prices, lower range (in dollars per share)	50.01
Range of exercise prices, upper range (in dollars per share)	$ 76.9
Outstanding (in shares) | shares	58,454
Weighted average remaining contractual life (in years)	7 years 1 month 6 days
Weighted average exercise price (in dollars per share)	$ 62.64
Number exercisable (in shares) | shares	17,485
Weighted average exercise price (in dollars per share)	$ 61.75
$76.91-86.18
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Range of exercise prices, lower range (in dollars per share)	76.91
Range of exercise prices, upper range (in dollars per share)	$ 86.18
Outstanding (in shares) | shares	222
Weighted average remaining contractual life (in years)	7 years 10 months 22 days
Weighted average exercise price (in dollars per share)	$ 86.18
Number exercisable (in shares) | shares	56
Weighted average exercise price (in dollars per share)	$ 86.18