Stock Based Compensation (Tables)

12 Months Ended

Dec. 31, 2018

Stock Based Compensation [Abstract]

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

The following is a summary of the key assumptions used in the valuation calculations for market based awards granted during the years ended December 31, 2018, 2017 and 2016:

	2018	2017	2016
Risk free rate	1.61% - 2.14%	0.65% - 1.57%	0.49% - 1.27%
Dividend yield	3.884%	3.573%	3.634%
Volatility	15.05% - 17.18%	20.43% - 21.85%	18.41% - 19.45%
Requisite service period	3 years	3 years	3 years

Nonvested Restricted Stock Shares Activity [Table Text Block]

A summary of the status of the nonvested restricted shares as of December 31, 2018, and the changes for the year ended December 31, 2018, is presented below:

Nonvested Shares	Shares		Weighted Average Grant-Date Fair Value
Nonvested as of January 1, 2018	180,692		$	81.13
Issued	115,177		89.67
Vested	(106,434	)	71.80
Forfeited	(1,658	)	90.30
Nonvested as of December 31, 2018	187,777		$	88.79

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

The following is a summary of the key assumptions used in the Monte Carlo valuation calculations for stock options granted during the year ended December 31, 2016:

	2016
Risk free rate	0.64% - 2.63%
Dividend yield	3.81%
Volatility	21.02% - 21.57%
Expected term	1.11 - 2.11 years

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

A summary of the status of the stock options as of December 31, 2018 and the changes for the year ended December 31, 2018 is presented below:

Stock Options	Options		Weighted Average Exercise Price
Outstanding as of January 1, 2018	108,438		$	72.93
Granted	—		—
Exercised	(17,823	)	51.42
Expired	—		—
Outstanding as of December 31, 2018	90,615		$	77.16