Shareholders' Equity and Common Stock Equivalents - Stock Option Information by Ranges of Exercise Prices (Details) - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Summary of options outstanding segregated by ranges of exercise prices
Total Outstanding Options, Options (in shares)	719,015	747,032	669,693
Total Outstanding Options, Weighted Average Option Price per Share (in usd per share)	$ 32.80	$ 27.67
Total Outstanding Options, Weighted Average Remaining Term	7 years 4 months 13 days
Vested and Exercisable Options (in shares)	258,321	273,117
Vested and Exercisable Options, Weighted Average Option Price per Share (in usd per share)	$ 27.12	$ 22.73	$ 19.32
Vested and Exercisable Options, Weighted Average Remaining Term	5 years 5 months 5 days
Minimum
Summary of options outstanding segregated by ranges of exercise prices
Total Outstanding Options, Weighted Average Option Price per Share (in usd per share)	$ 17.01
Maximum
Summary of options outstanding segregated by ranges of exercise prices
Total Outstanding Options, Weighted Average Option Price per Share (in usd per share)	$ 41.95
Range One
Summary of options outstanding segregated by ranges of exercise prices
Total Outstanding Options, Options (in shares)	78,774
Total Outstanding Options, Weighted Average Option Price per Share (in usd per share)	$ 19.30
Total Outstanding Options, Weighted Average Remaining Term	1 year 6 months 18 days
Vested and Exercisable Options (in shares)	78,774
Vested and Exercisable Options, Weighted Average Option Price per Share (in usd per share)	$ 19.30
Vested and Exercisable Options, Weighted Average Remaining Term	1 year 6 months 18 days
Range One | Minimum
Summary of options outstanding segregated by ranges of exercise prices
Total Outstanding Options, Weighted Average Option Price per Share (in usd per share)	$ 17.01
Range One | Maximum
Summary of options outstanding segregated by ranges of exercise prices
Total Outstanding Options, Weighted Average Option Price per Share (in usd per share)	$ 22.69
Range Two
Summary of options outstanding segregated by ranges of exercise prices
Total Outstanding Options, Options (in shares)	424,057
Total Outstanding Options, Weighted Average Option Price per Share (in usd per share)	$ 30.81
Total Outstanding Options, Weighted Average Remaining Term	7 years 6 months 10 days
Vested and Exercisable Options (in shares)	177,686
Vested and Exercisable Options, Weighted Average Option Price per Share (in usd per share)	$ 30.49
Vested and Exercisable Options, Weighted Average Remaining Term	7 years 1 month 13 days
Range Two | Minimum
Summary of options outstanding segregated by ranges of exercise prices
Total Outstanding Options, Weighted Average Option Price per Share (in usd per share)	$ 28.88
Range Two | Maximum
Summary of options outstanding segregated by ranges of exercise prices
Total Outstanding Options, Weighted Average Option Price per Share (in usd per share)	$ 33.41
Range Three
Summary of options outstanding segregated by ranges of exercise prices
Total Outstanding Options, Options (in shares)	216,184
Total Outstanding Options, Weighted Average Option Price per Share (in usd per share)	$ 41.62
Total Outstanding Options, Weighted Average Remaining Term	9 years 2 months 1 day
Vested and Exercisable Options (in shares)	1,861
Vested and Exercisable Options, Weighted Average Option Price per Share (in usd per share)	$ 36.04
Vested and Exercisable Options, Weighted Average Remaining Term	8 years 8 months 23 days
Range Three | Minimum
Summary of options outstanding segregated by ranges of exercise prices
Total Outstanding Options, Weighted Average Option Price per Share (in usd per share)	$ 36.04
Range Three | Maximum
Summary of options outstanding segregated by ranges of exercise prices
Total Outstanding Options, Weighted Average Option Price per Share (in usd per share)	$ 41.95