Stock Based Compensation (Tables)

12 Months Ended

Dec. 31, 2016

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]

		2016		2015		2014
Stock options	$	848	$	730	$	663
Nonvested stock awards and restricted stock units		3,121		2,937		2,473
Employee stock purchase plan		87		75		73
Non-elective and elective 401(k) matching contribution in stock		2,124		2,052		1,975
Director stock ownership plan		169		125		125
Total share-based compensation expense	$	6,349	$	5,919	$	5,309

Schedule of Share-based Compensation, Stock Options, Activity [Table Text Block]

			Weighted		Weighted
			Average		Average
			Exercise		Remaining	Aggregate
		Number of	Price		Contractual	Intrinsic
		Options	(per option)		Term (years)	Value
Options outstanding at January 1, 2016		99,671	$	71.73
	Options granted	67,444		72.12
	Options exercised	(49,895)		63.78
Options outstanding at December 31, 2016		117,220	$	75.34	5.5	$	6,203
Options expected to vest after December 31, 2016		103,040	$	75.82	5.7	$	5,403
Options exercisable at December 31, 2016		14,180	$	71.87	4.1	$	800

Schedule of Share-based Compensation, Shares Authorized under Stock Option Plans, by Exercise Price Range [Table Text Block]

						Weighted
						Average	Weighted			Weighted
					Number	Remaining	Average		Number	Average
Range of					of Options	Contractual	Exercise Price		of Options	Exercise Price
Exercise Prices					Outstanding	Term (years)	(per option)		Exercisable	(per option)
$	30.01	-	$	40.00	552	2.2	$	38.13	552	$	38.13
$	40.01	-	$	50.00	—	—		—	—		—
$	50.01	-	$	60.00	3,714	3.2		58.26	3,714		52.26
$	60.01	-	$	70.00	—	—		—	—		—
$	70.01	-	$	80.00	85,009	5.7		72.40	6,060		73.47
$	80.01	-	$	90.00	27,945	5.1		87.30	3,854		87.30
					117,220	5.5		75.34	14,180		71.87

Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions [Table Text Block]

	2016		2015		2014		2013
Number of stock options granted	67,444		38,698		37,048		29,302
Dividend yield	1.49	%	1.55	%	2.00	%	2.49	%
Expected volatility	28.39	%	36.32	%	43.34	%	57.28	%
Risk-free interest rate	1.08	%	1.22	%	1.22	%	0.63	%
Expected term (years)	4.0		4.0		4.0		4.0

Schedule of Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Table Text Block]

		2016		2015		2014
2016 Stock option awards	$	282	$	—	$	—
2015 Stock option awards	$	276	$	232	$	—
2014 Stock option awards	$	254	$	257	$	227
2013 Stock option awards	$	36	$	200	$	213

Schedule of Share-based Compensation, Restricted Stock and Restricted Stock Units Activity [Table Text Block]

		Weighted
		Average Grant
	Number of	Date Fair Value
	Shares	(per share)
Nonvested awards, December 31, 2015	113,910	$	72.91
Granted	29,271	$	76.33
Vested	(32,604)	$	64.84
Forfeited	(1,494)	$	73.07
Nonvested awards, December 31, 2016	109,083	$	76.23

Schedule of Share-based Compensation, Restricted Stock Units Award Activity [Table Text Block]

		Weighted
		Average Grant
	Number of	Date Fair Value
	Units	(per unit)
Nonvested awards, December 31, 2015	6,174	$	74.14
Granted	2,141	$	77.10
Vested	(2,252)	$	64.54
Forfeited	(292)	$	79.96
Nonvested awards, December 31, 2016	5,771	$	78.69