Shareholders' Equity and Common Stock Equivalents (Details 1) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Summary of changes in outstanding options
Weighted Average Option Price per Share, Beginning Balance	$ 17.49
Weighted Average Option Price per Share, Options Granted	$ 28.88
Weighted Average Option Price per Share, Options Vested	$ 17.78
Weighted Average Option Price per Share, Options Exercised	$ 16.50
Weighted Average Option Price per Share, Options Forfeited	$ 18.53
Weighted Average Option Price per Share, Options Expired	$ 0
Weighted Average Option Price per Share, Ending Balance	$ 21.22	$ 17.49
Range of Option Prices per Share, Expired	$ 0
Options Outstanding, Beginning Balance	956,814	1,882,939
Options Outstanding, Granted	175,632	245,424	296,188
Options Outstanding, Vested	0
Options Outstanding, Exercised	(435,665)	(1,158,537)	(389,089)
Options Outstanding, Forfeited	(62,344)
Options Outstanding, Expired	0
Options Outstanding, Ending Balance	634,437	956,814	1,882,939
Options Vested and Exercisable, Beginning Balance	314,445
Options Vested and Exercisable, Granted	0
Options Vested and Exercisable, Vested	392,142
Options Vested and Exercisable, Exercisable	(435,665)
Options Vested and Exercisable, Forfeited	(62,344)
Options Vested and Exercisable, Expired	0
Options Vested and Exercisable, Ending Balance	208,578	314,445
Maximum [Member]
Summary of changes in outstanding options
Range of Option Prices per Share, Beginning Balance	$ 30.24
Range of Option Prices per Share, Granted	$ 28.91
Range of Option Prices per Share, Vested	$ 30.24
Range of Option Prices per Share, Exercised	$ 22.69
Range of Option Prices per Share, Forfeited	$ 20.60
Range of Option Prices per Share, Ending Balance	$ 30.24
Minimum [Member]
Summary of changes in outstanding options
Range of Option Prices per Share, Beginning Balance	$ 6.91
Range of Option Prices per Share, Granted	$ 28.88
Range of Option Prices per Share, Vested	$ 13.83
Range of Option Prices per Share, Forfeited	$ 13.83
Range of Option Prices per Share, Ending Balance	$ 6.91
Options Outstanding, Exercised	6.91