Shareholders' Equity and Common Stock Equivalents - Stock Option Activity (Details) - $ / shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Weighted Average Option Price per Share
Weighted Average Option Price per Share, Beginning Balance (in usd per share)	$ 32.80
Weighted Average Option Price per Share, Options Granted (in usd per share)	43.04
Weighted Average Option Price per Share, Options Vested (in usd per share)	31.42
Weighted Average Option Price per Share, Options Exercised (in usd per share)	27.07
Weighted Average Option Price per Share, Options Forfeited (in usd per share)	39.07
Weighted Average Option Price per Share, Options Expired (in usd per share)	0
Weighted Average Option Price per Share, Ending Balance (in usd per share)	$ 36.65	$ 32.80
Outstanding
Options Outstanding, Beginning Balance (in shares)	719,015	747,032
Options Outstanding, Granted (in shares)	223,208	222,828	307,176
Options Outstanding, Vested (in shares)	0
Options Outstanding, Exercised (in shares)	(145,438)
Options Outstanding, Forfeited (in shares)	(21,964)
Options Outstanding, Expired (in shares)	0
Options Outstanding, Ending Balance (in shares)	774,821	719,015	747,032
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Exercisable [Roll Forward]
Options Vested and Exercisable, Beginning Balance (in shares)	258,321
Options Vested and Exercisable, Granted (in shares)	0
Options Vested and Exercisable, Vested (in shares)	158,233
Options Vested and Exercisable, Exercisable (in shares)	(145,438)
Options Vested and Exercisable, Forfeited (in shares)	0
Options Vested and Exercisable, Expired (in shares)	0
Options Vested and Exercisable, Ending Balance (in shares)	271,116	258,321
Minimum
Weighted Average Option Price per Share
Weighted Average Option Price per Share, Ending Balance (in usd per share)	$ 41.95
Share-based Compensation Arrangement by Share-based Payment Award, Options, Range of Option Prices [Roll Forward]
Range of Option Prices per Share, Beginning Balance (in usd per share)	17.01
Range of Option Prices per Share, Granted (in usd per share)	42.95
Range of Option Prices per Share, Vested (in usd per share)	17.32
Range of Option Prices per Share, Exercised (in usd per share)	17.01
Range of Option Prices per Share, Forfeited (in usd per share)	31.01
Range of Option Prices per Share, Expired (in usd per share)	0
Range of Option Prices per Share, Ending Balance (in usd per share)	17.32	$ 17.01
Maximum
Weighted Average Option Price per Share
Weighted Average Option Price per Share, Ending Balance (in usd per share)	44.75
Share-based Compensation Arrangement by Share-based Payment Award, Options, Range of Option Prices [Roll Forward]
Range of Option Prices per Share, Beginning Balance (in usd per share)	41.95
Range of Option Prices per Share, Granted (in usd per share)	44.75
Range of Option Prices per Share, Vested (in usd per share)	41.95
Range of Option Prices per Share, Exercised (in usd per share)	41.95
Range of Option Prices per Share, Forfeited (in usd per share)	42.95
Range of Option Prices per Share, Expired (in usd per share)	0
Range of Option Prices per Share, Ending Balance (in usd per share)	$ 44.75	$ 41.95