Shareholders' Equity and Common Stock Equivalents - Stock Option Activity (Details) - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Weighted Average Option Price per Share
Weighted Average Option Price per Share, Beginning Balance (in usd per share)	$ 27.67
Weighted Average Option Price per Share, Options Granted (in usd per share)	41.83
Weighted Average Option Price per Share, Options Vested (in usd per share)	27.12
Weighted Average Option Price per Share, Options Exercised (in usd per share)	23.63
Weighted Average Option Price per Share, Options Forfeited (in usd per share)	34.97
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)	$ 32.80	$ 27.67
Outstanding
Options Outstanding, Beginning Balance (in shares)	747,032	669,693
Options Outstanding, Granted (in shares)	222,828	307,176	142,908
Options Outstanding, Vested (in shares)	0
Options Outstanding, Exercised (in shares)	(208,306)
Options Outstanding, Forfeited (in shares)	(42,539)
Options Outstanding, Expired (in shares)	0
Options Outstanding, Ending Balance (in shares)	719,015	747,032	669,693
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Exercisable [Roll Forward]
Options Vested and Exercisable, Beginning Balance (in shares)	273,117
Options Vested and Exercisable, Granted (in shares)	0
Options Vested and Exercisable, Vested (in shares)	193,510
Options Vested and Exercisable, Exercisable (in shares)	(208,306)
Options Vested and Exercisable, Forfeited (in shares)	0
Options Vested and Exercisable, Expired (in shares)	0
Options Vested and Exercisable, Ending Balance (in shares)	258,321	273,117
Minimum
Weighted Average Option Price per Share
Weighted Average Option Price per Share, Ending Balance (in usd per share)	$ 17.01
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)	13.83
Range of Option Prices per Share, Granted (in usd per share)	38.05
Range of Option Prices per Share, Vested (in usd per share)	17.01
Range of Option Prices per Share, Exercised (in usd per share)	13.83
Range of Option Prices per Share, Forfeited (in usd per share)	28.88
Range of Option Prices per Share, Expired (in usd per share)	0
Range of Option Prices per Share, Ending Balance (in usd per share)	17.01	$ 13.83
Maximum
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)	36.04
Range of Option Prices per Share, Granted (in usd per share)	41.95
Range of Option Prices per Share, Vested (in usd per share)	36.04
Range of Option Prices per Share, Exercised (in usd per share)	32.35
Range of Option Prices per Share, Forfeited (in usd per share)	41.95
Range of Option Prices per Share, Expired (in usd per share)	0
Range of Option Prices per Share, Ending Balance (in usd per share)	$ 41.95	$ 36.04