Cash and stock-based compensation plans (Details Textual) (USD $)	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Exercised stock options	$ 1,469,000	$ 3,702,000	$ 13,136,000
Deferred Compensation Plan (Dc Plan) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated Share-based Compensation Expense		0	1,000
Stock Purchase Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock Based Compensation Vesting Rate	25.00%
Allocated Share-based Compensation Expense	242,000	282,000	485,000
Unallocated Share Based Compensation Expense	601,000
Exercisable Aggregate intrinsic value	493,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Total Intrinsic Value	1,911,000	2,673,000	3,375,000
Exercised stock options	1,470,000	2,886,000	5,709,000
Unamortized Compensation Cost Amortization Period	3 years 1 month 13 days
Stock Option Plan 2006 - Directors and Executives [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Exercisable Aggregate intrinsic value		442,000	570,000
Exercised stock options		814,000	2,130,000
Indexed Stock Option Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Exercisable Aggregate intrinsic value			1,213,000
Exercised stock options			5,292,000
Restricted Stock Directors [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock Granted During Period, Shares, Share-based Compensation	28,500	28,500	32,317
Stock Based Compensation Grants Fair Value	862,000	713,000	714,000
Allocated Share-based Compensation Expense	846,000	637,000	428,000
Unallocated Share Based Compensation Expense	1,417,000
Vested Aggregate Fair Value	659,000	581,000	337,000
Unamortized Compensation Cost Amortization Period	2 years 7 days
Restricted Stock Units and Stock Purchase Options Granted To Certain Executives [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock Based Compensation Vesting Rate	25.00%
Stock Based Compensation Grants Fair Value	1,600,000	2,100,000	3,700,000
Allocated Share-based Compensation Expense	1,158,000	2,077,000	1,317,000
Unallocated Share Based Compensation Expense	1,966,000
Vested Aggregate Fair Value	1,424,000	2,002,000	1,050,000
Distribution Of The Fair Value In Restricted Stock Units	900,000		3,200,000
Distribution Of The Fair Value In Stock Purchase Options	700,000		500,000
Unamortized Compensation Cost Amortization Period	2 years 1 month 28 days
Other Plans Expatriate Officer Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Salaries, Wages and Officers' Compensation	133,000	120,000	131,000
Accounts Payable and Accrued Liabilities	222,000	176,000
Restricted Stock Directors (Discontinued) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock Based Compensation Vesting Rate	20.00%
Allocated Share-based Compensation Expense			41,000
Vested Aggregate Fair Value			$ 75,000

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It represents Distribution Of The Fair Value In Stock Purchase Options.

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The rate at which restricted stock and options are vested in each year, beginning the year following the grant.

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Unamortized stock based compensation

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Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

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The cash inflow associated with the amount received from holders exercising their stock options. This item inherently excludes any excess tax benefit, which the entity may have realized and reported separately.

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Expenditures for salaries for officers and non-officers. Does not include allocated share-based compensation, pension and post-retirement benefit expense or other labor-related non-salary expense. For commercial and industrial companies, excludes any direct and overhead labor that is included in cost of goods sold.

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Fair value of share-based awards for which the grantee gained the right by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash.

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Amount of difference between fair value of the underlying shares reserved for issuance and exercise price of vested portions of options outstanding and currently exercisable.

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Amount of accumulated difference between fair value of underlying shares on dates of exercise and exercise price on options exercised (or share units converted) into shares.

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Gross number of shares (or other type of equity) issued during the period as a result of any equity-based compensation plan other than an employee stock ownership plan (ESOP). Shares issued could result from the issuance of restricted stock, the exercise of stock options, stock issued under employee stock purchase plans, and/or other employee benefit plans.

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Gross value of stock (or other type of equity) issued during the period as a result of any equity-based compensation plan other than an employee stock ownership plan (ESOP). Stock issued could result from the issuance of restricted stock, the exercise of stock options, stock issued under employee stock purchase plans, and/or other employee benefit plans.

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