Stock Based Compensation (Tables)

12 Months Ended

Dec. 31, 2016

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, 2016, 2015, and 2014:

	2016	2015	2014
Risk free rate - minimum	0.49%	0.10%	0.02%
Risk free rate - maximum	1.27%	1.05%	0.80%
Dividend yield	3.634%	3.932%	4.755%
Volatility - minimum	18.41%	15.41%	18.31%
Volatility - maximum	19.45%	16.04%	20.48%
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, 2016, and the changes for the year ended December 31, 2016, is presented below:

Nonvested Shares	Shares		Weighted Average Grant-Date Fair Value
Nonvested at January 1, 2016	187,941		$	63.36
Issued	119,039		79.51
Vested	(80,342	)	64.00
Forfeited	(1,014	)	71.84
Nonvested at December 31, 2016	225,624		$	71.61

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
Term - minimum	1.11 years
Term - maximum	2.11 years
Risk free rate - minimum	0.64%
Risk free rate - maximum	2.63%
Dividend yield	3.81%
Volatility - minimum	21.02%
Volatility - maximum	21.57%

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

A summary of the status of the stock options as of December 31, 2016 and the changes for the year ended December 31, 2016 is presented below:

Stock Options	Options		Weighted Average Exercise Price
Outstanding at January 1, 2016	58,112		$	86.21
Granted	108,198		75.58
Exercised	—		—
Expired	(19,028	)	103.56
Outstanding at December 31, 2016	147,282		$	76.16