Equity (Details 2) - $ / shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Options
Shares under option - beginning of year	730,980	684,540	709,300
Options granted	196,350	174,600	148,950
Options exercised	(140,579)	(103,230)	(123,150)
Options forfeited	(10,580)	(24,930)	(50,560)
Shares under option - end of year	776,171	730,980	684,540
Weighted Average Exercise Price
Shares under option - beginning of year	$ 31.92	$ 26.94	$ 24.34
Options granted	63.91	43.48	32.61
Options exercised	24.21	19.03	18.69
Options forfeited	37.64	29.49	27.18
Shares under option - end of year	$ 41.33	$ 31.92	$ 26.94