Stock Based Compensation (Awards of Restricted Stock) (Details)	9 Months Ended
	Sep. 30, 2015 $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares Granted	21,780
Grant Date Fair Value | $ / shares	$ 40.03
2/11/2015 | 2005 Employee Stock Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares Granted	31,500
Grant Date Fair Value | $ / shares	$ 39.42
Vesting Period	Ratably over 5 years from grant date
2/12/2015 | 2005 Employee Stock Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares Granted	25,910
Grant Date Fair Value | $ / shares	$ 40.03
Vesting Period	Ratably over 5 years from grant date
3/19/2015 | 2005 Employee Stock Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares Granted	3,800
Grant Date Fair Value | $ / shares	$ 43.56
Vesting Period	Ratably over 5 years from grant date
4/27/2015 | 2005 Employee Stock Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares Granted	625
Grant Date Fair Value | $ / shares	$ 41.61
Vesting Period	At the end of 3 years from grant date
4/27/2015 | 2005 Employee Stock Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares Granted	1,875
Grant Date Fair Value | $ / shares	$ 41.61
Vesting Period	At the end of 5 years from grant date
5/27/2015 | 2010 Non-Employee Director Stock Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares Granted	8,800
Grant Date Fair Value | $ / shares	$ 45.02
Vesting Period	At the end of 5 years from grant date
7/14/2015 | 2010 Non-Employee Director Stock Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares Granted	800
Grant Date Fair Value | $ / shares	$ 47.82
Vesting Period	Once on May 27, 2020