Stock Compensation (Narrative) (Details)	12 Months Ended
	Dec. 31, 2015 USD ($) item $ / shares shares	Dec. 31, 2014 USD ($) $ / shares shares	Dec. 31, 2013 USD ($) $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options and restricted stock units authorized to grant	1,300,000
Proceeds from the exercise of stock options | $	$ 5,089,000	$ 3,054,000	$ 4,682,000
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period (in years)	5 years
Vesting percentage, year one	20.00%
Vesting percentage, year two	20.00%
Vesting percentage, year three	20.00%
Vesting percentage, year four	20.00%
Vesting percentage, year five	20.00%
Expiration period (in years)	10 years
Weighted average grant date fair value of options granted | $ / shares	$ 8.49	$ 10.95	$ 9.18
Dividend yield	2.50%	2.30%	2.20%
Expected volatility	16.10%	17.70%	17.50%
Expected life (in years)	5 years	5 years	5 years
Risk-free interest rate	1.40%	1.70%	1.00%
Stock options expense | $	$ 261,000	$ 1,100,000	$ 425,000
Unamortized compensation expense | $	$ 412,000
Weighted average recognized period of unamortized compensation expenses (in years)	3 years
Exercise of stock options, shares	99,178	61,273	97,800
Aggregate intrinsic value of the stock options exercised | $	$ 2,600,000	$ 2,100,000	$ 3,100,000
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period (in years)	6 years
Vesting percentage, year one	0.00%
Vesting percentage, year two	20.00%
Vesting percentage, year three	20.00%
Vesting percentage, year four	20.00%
Vesting percentage, year five	20.00%
Vesting percentage, year six	20.00%
Restricted stock units granted	75,606	6,800	8,350
Weighted average grant date fair value of stock granted | $ / shares	$ 82.78	$ 81.47	$ 73.85
Restricted stock units expense | $	$ 433,000	$ 526,000	$ 671,000
Unamortized compensation expense | $	$ 20,200,000
Weighted average recognized period of unamortized compensation expenses (in years)	4 years 3 months 18 days
Number of units vested	25,384	12,980	13,690
Number of units issued	15,734	8,066	8,547
Aggregate fair value of the shares vested | $	$ 2,000,000	$ 1,100,000	$ 1,000,000
Special Cash Dividend [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options expense | $		644,000
2003 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares covered under Stock Option and Incentive Plan	1,500,000
2012 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares covered under Stock Option and Incentive Plan	1,000,000
Vesting period (in years)	5 years
Expiration period (in years)	10 years
2014 Performance-Based Restricted Stock Unit Program [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock units granted	66,506
Weighted average grant date fair value of stock granted | $ / shares	$ 83.47
Number of defined targets to achieve for restricted stock unit awards, maximum | item	3
Number of defined targets to achieve for restricted stock unit awards, minimum | item	1
Length of Restricted Stock Unit program (in years)	4 years
Number of annual vesting installments | item	4
Approximate number of restricted stock units granted per year, maximum	96,650
Maximum shares for cumulative four-year period	82,846
Compensation expense | $	$ 8,200,000	7,400,000
Unamortized compensation expense | $	$ 18,500,000
Number of units vested	16,634
Number of units issued	10,495
Aggregate fair value of the shares vested | $	$ 1,300,000
2012 Performance-Based Restricted Stock Unit Program [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Reversal of LTEIP amortization | $			3,900,000
Retirement Plan For Non-Employee Directors [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense | $	316,000	550,000	264,000
Additional compensation expense | $	243,000
Unamortized compensation expense | $	$ 1,200,000	$ 1,500,000	$ 1,400,000
Number of units issued	0	0	0
Shares approved for issuance	130,000
Number of shares granted for each year served	1,000
Maximum number of shares issued upon retirement	8,000