Share-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2017

Deferred Compensation Arrangements [Abstract]

Schedule of Stock Option Valuation Assumptions [Table Text Block]

The fair value of each grant is estimated on the date of grant using the Black-Scholes option-pricing model with the following weighted average assumptions:

	2017	2016	2015
Dividend yield	5.3%	6.2%	4.7%
Expected volatility	19.8%	19.1%	17.8%
Expected lives	2.9 years	2.9 years	2.8 years
Risk-free interest rate	1.49%	0.91%	0.98%

Schedule of Stock Option Activity [Table Text Block]

The following tables summarize our outstanding stock options:

				Weighted Average
	Number		Weighted Average	Remaining	Aggregate
	of Shares		Exercise Price	Contractual Life (Years)	Intrinsic Value
Outstanding December 31, 2014	871,671		$60.43
Options granted under 2012 Plan	450,000		$72.11
Options granted under 2005 Plan	20,000		$72.11
Options exercised under 2005 Plan	(66,670	)	$46.87
Options exercised under 2012 Plan	(421,657	)	$63.03
Options canceled under 2012 Plan	(111,668	)	$71.95
Outstanding December 31, 2015	741,676		$60.43
Options granted under 2012 Plan	470,000		$60.78
Options exercised under 2005 Plan	(61,666	)	$52.36
Options exercised under 2012 Plan	(608,331	)	$65.18
Outstanding December 31, 2016	541,679		$65.84
Options granted under 2012 Plan	495,000		$74.90
Options exercised under 2005 Plan	(15,000	)	$47.52
Options exercised under 2012 Plan	(155,829	)	$65.73
Options canceled under 2012 Plan	(6,668	)	$60.52
Outstanding December 31, 2017	859,182		$70.11	3.39	$	4,531,000
Exercisable December 31, 2017	465,831		$69.85	3.01	$	2,578,000

				Remaining
Grant	Number	Exercise		Contractual
Date	of Shares	Price		Life in Years
2/25/2013	15,000	$	64.49	0.15
2/25/2014	48,334	$	61.31	1.15
2/20/2015	120,004	$	72.11	2.14
2/22/2016	185,842	$	60.52	3.15
3/8/2016	26,667	$	63.63	3.19
2/22/2017	453,335	$	74.78	4.15
9/1/2017	10,000	$	80.55	4.68
Outstanding December 31, 2017	859,182

Schedule of Nonvested Share Activity [Table Text Block]

The following table summarizes our outstanding non-vested stock options:

	Number of Shares		Weighted Average Grant Date Fair Value
Non-vested December 31, 2016	353,348		$3.99
Options granted under 2012 Plan	495,000		$5.76
Options vested under 2012 Plan	(441,661	)	$4.98
Options vested under 2005 Plan	(6,668	)	$4.91
Non-vested options canceled under 2012 Plan	(6,668	)	$3.61
Non-vested December 31, 2017	393,351		$5.10