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Share Based Compensation (Tables)
12 Months Ended
Dec. 31, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]  
Schedule of Compensation Cost for Share-based Payment Arrangements, Allocation of Share-based Compensation Costs by Plan [Table Text Block]
201720162015
Stock options$958$848$730
Nonvested stock awards and restricted stock units2,9353,1212,937
Employee stock purchase plan888775
Non-elective and elective 401(k) matching contribution in stock722,1242,052
Director stock ownership plan137169125
Total share-based compensation expense$4,190$6,349$5,919
Schedule of Share-based Compensation, Stock Options, Activity [Table Text Block]
Weighted Weighted
AverageAverage
Exercise RemainingAggregate
Number ofPrice ContractualIntrinsic
Options(per option)Term (years)Value
Options outstanding as of January 1, 2017117,220$75.34
Options granted42,477134.60
Options exercised(48,442)75.94
Options outstanding as of December 31, 2017111,255$97.715.3$6,013
Options expected to vest after December 31, 201799,484$100.645.5$5,086
Options exercisable as of December 31, 201711,771$72.953.9$928
Schedule of Share-based Compensation, Shares Authorized under Stock Option Plans, by Exercise Price Range [Table Text Block]
Weighted
AverageWeightedWeighted
NumberRemainingAverageNumberAverage
Range ofof OptionsContractualExercise Priceof OptionsExercise Price
Exercise PricesOutstandingTerm (years)(per option)Exercisable(per option)
$30.01 -$40.00 5521.2$38.13552$38.13
$40.01 -$50.00
$50.01 -$60.00 8742.258.2687458.26
$60.01 -$70.00
$70.01 -$80.00 52,9465.072.217,98472.72
$80.01 -$90.00 14,4064.287.302,36187.30
$90.01 -$130.00
$130.01 -$140.00 42,4776.2134.60
111,2555.397.7111,77172.95
Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions [Table Text Block]
2017201620152014
Number of stock options granted42,47767,44438,69837,048
Dividend yield1.49%1.49%1.55%2.00%
Expected volatility25.52%28.39%36.32%43.34%
Risk-free interest rate1.67%1.08%1.22%1.22%
Expected term (years)4.04.04.04.0
Schedule of Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Table Text Block]
201720162015
2017 Stock option awards$308$$
2016 Stock option awards$332$282$
2015 Stock option awards$276$276$232
2014 Stock option awards$42$254$257
Schedule of Share-based Compensation, Restricted Stock and Restricted Stock Units Activity [Table Text Block]
Weighted
Average Grant
Number ofDate Fair Value
Shares(per share)
Nonvested awards, December 31, 2016109,083$76.23
Granted17,315$136.18
Vested(53,749)$75.68
Forfeited(485)$76.41
Nonvested awards, December 31, 201772,164$91.03
Schedule of Share-based Compensation, Restricted Stock Units Award Activity [Table Text Block]
Weighted
Average Grant
Number ofDate Fair Value
Units(per unit)
Nonvested awards, December 31, 20165,771$78.69
Granted1,332$134.60
Vested(2,702)$78.37
Forfeited(124)$105.38
Nonvested awards, December 31, 20174,277$95.53