Stock Options (Schedule of Restricted Stock Award Activity) (Details) - Restricted Stock - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Outstanding at beginning of year (in shares)	45,621	32,616	12,043
Granted (in shares)	33,620	27,440	26,004
Exercised (in shares)	(16,189)	(11,909)	(5,431)
Canceled (in shares)	0	(2,526)	0
Outstanding at end of year (in shares)	63,052	45,621	32,616
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Intrinsic Value [Roll Forward]
Outstanding at beginning of year (in dollars per share)	$ 54.58	$ 53.31	$ 44.10
Granted (in dollars per share)	84.34	55.17	54.14
Exercised (in dollars per share)	56.03	52.67	36.85
Canceled (in dollars per share)	0.00	53.57	0.00
Outstanding at end of year (in dollars per share)	$ 70.08	$ 54.58	$ 53.31