Stock Based Compensation - Options Rollforward (Details) (USD $)	6 Months Ended
	Jun. 30, 2013
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Beginning Balance	107,455
Options Granted	29,302
Options Exercised	(23,415)
Options Forfeited	(3,601)
Options Expired	(768)
Ending Balance	108,973
Options Exerciseable	45,562
Weighted Average Exercise Price [Abstract]
Outstanding at Beginning of Year	$ 31.23
Options Granted	$ 58.26
Options Exercised	$ 25.10
Options Forfeited	$ 37.81
Options Expired	$ 37.37
Outstanding at End of Period	$ 39.55
Options Exercisable	$ 28.50
Weighted Average Contractual Term [Abstract]
Weighted Average Remaining Contractual Term, Outstanding	5 years 4 months
Weighted Average Remaining Contractual Term, Exercisable	4 years 4 months