Cash and stock-based compensation plans (Tables)

12 Months Ended

Dec. 31, 2017

Disclosure of share-based payment arrangements [Abstract]

Disclosure of detailed information about restricted stock option to directors [Text Block]

A summary of the restricted stock granted to Directors is presented below:

	Shares		Weighted average grant date fair value
Outstanding at January 1, 2015		78,336		24.37
Granted		57,000		33.78
Vested		(39,015)		22.69
Outstanding at December 31, 2015		96,321		30.62
Granted		57,000		24.14
Vested		(56,421)		28.80
Outstanding at December 31, 2016		96,900		27.86
Granted		57,000		27.80
Vested		(61,950)		28.50
Outstanding at December 31, 2017		91,950		27.40
Expected to vest		91,950

Disclosure of number and weighted average exercise prices of other equity instruments [text block]

A summary of the restricted stock units granted to certain executives is presented below:

	Shares		Weighted average grand date fair value		Weighted average remaining contractual term		Aggregate Intrinsic value
Outstanding at January 1, 2015		163,712		18.18
Granted		63,244		21.67
Forfeited		-
Vested		(64,208)		17.67
Outstanding at December 31, 2015		162,748		19.74
Granted		91,454		18.26
Forfeited		(21,408)		17.69
Vested		(65,358)		18.83
Outstanding at December 31, 2016		167,436		19.35
Granted		25,289		25.70
Forfeited		(71,401)		18.61
Vested		(70,519)		19.76
Outstanding at December 31, 2017		50,805		21.07		2.02 years	$	518
Expected to vest		50,805		21.07		2.02 years	$	296

Disclosure of detailed information about share options granted to executives [Text Block]

The fair value of stock purchase options granted to certain Executives during 2017 was estimated using a binomial option-pricing model, based on the following factors:

	Measuring unit	2017		2016		2015

Weighted average fair value per option	$		-		-		1.95 - 2.06
Weighted average expected term, in years	Year		-		-		5.5
Expected volatility	%		-		-		22	%
Risk-free rate	%		-		-		0.02 – 1.52
Expected dividend	%		-		-		5.00	%

Disclosure of detailed information about share options granted [Text Block]

A summary of stock options granted is presented below:

	Options		Weighted average exercise price		Weighted average remaining contractual term		Aggregate Intrinsic value
Outstanding at January 1, 2015		391,696		23.65
Granted		233,418		29.25
Forfeited		-		-
Exercised		(70,358)		20.86
Outstanding at December 31, 2015		554,756		26.36
Granted		-		-
Forfeited		(126)		18.93
Exercised		(68,785)		22.78
Outstanding at December 31, 2016		485,845		26.87
Granted		-
Forfeited		(69,934)		28.63
Exercised		(142,268)		24.84
Outstanding at December 31, 2017		273,643		27.48		3.66 years	$	242
Exercisable		121,840		27.73		3.70 years	$	115
Expected to vest		151,803		27.28		3.63 years	$	128