Stock-Based Compensation (Number, Weighted Average Exercise Price and Weighted Average Remaining Contractual Life of Options Outstanding) (Details)	12 Months Ended
	Dec. 31, 2017 $ / shares shares
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Number of Options (in shares) | shares	105,994
Weighted Average Exercise Price (in dollars per share)	$ 42.95
Weighted Average Remaining Contractual Life (Years)	2 years 18 days
$27.00 - $38.00
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Range of Exercise Prices Lower Limit (in dollars per share)	$ 27.00
Range of Exercise Prices Upper Limit (in dollars per share)	$ 38.00
Number of Options (in shares) | shares	6,194
Weighted Average Exercise Price (in dollars per share)	$ 27.70
Weighted Average Remaining Contractual Life (Years)	1 year 1 month 28 days
$38.01 - $42.00
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Range of Exercise Prices Lower Limit (in dollars per share)	$ 38.01
Range of Exercise Prices Upper Limit (in dollars per share)	$ 42.00
Number of Options (in shares) | shares	2,300
Weighted Average Exercise Price (in dollars per share)	$ 41.79
Weighted Average Remaining Contractual Life (Years)	1 month 24 days
$42.01 - $45.00
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Range of Exercise Prices Lower Limit (in dollars per share)	$ 42.01
Range of Exercise Prices Upper Limit (in dollars per share)	$ 45.00
Number of Options (in shares) | shares	97,500
Weighted Average Exercise Price (in dollars per share)	$ 43.95
Weighted Average Remaining Contractual Life (Years)	2 years 1 month 24 days