CONCENTRATION OF RISK: (Tables)

12 Months Ended

Dec. 31, 2018

CONCENTRATION OF RISK:

Schedule of concentration risk for cash equivalents and short- term investments

	$ in		% of total		% in one institution
Country	million		cash (1)		of country		of total cash
United States	$	697.1	65.9	%	27.7	%	18.3	%
Switzerland		315.7	29.8	%	61.2	%	18.3	%
Peru		7.6	0.7	%	75.6	%	0.5	%
Mexico		38.0	3.6	%	89.3	%	3.2	%
Total cash and short-term investment	$	1,058.4	100.0	%

(1) 95.8% of the Company’s cash is in U.S. dollars.

Schedule of company's largest customers as percentage of accounts receivable and total sales

	2018		2017		2016
Accounts receivable trade as of December 31,
Five largest customers	34.2	%	28.4	%	31.1	%
Largest customer	10.9	%	8.2	%	11.9	%
Total sales in year
Five largest customers	28.4	%	25.1	%	30.4	%
Largest customer	9.3	%	8.8	%	8.4	%