Cash and stock-based compensation plans (Details 5) (Stock Option Plan 2006 - Directors and Executives [Member], USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Stock Option Plan 2006 - Directors and Executives [Member]
Options Outstanding	180,154	207,706	207,706
Forfeited Options	0	0	0
Exercised Options	(130,350)	(27,552)
Options Outstanding	49,804	180,154	207,706
Exercisable Options	49,804
Outstanding weighted average exercise price	$ 16.34	$ 16.34	$ 16.34
Forfeited Weighted average exercise price	$ 0	$ 0	$ 0
Outstanding weighted average exercise price	$ 16.34	$ 16.34	$ 16.34
Exercised Weighted average exercise price	$ 16.34	$ 16.34
Exercisable Weighted average exercise price	$ 16.34
Outstanding Weighted Average remaining contractual term	1 year 1 month 13 days
Exercisable Weighted Average remaining contractual term	1 year 1 month 13 days
Outstanding Aggregate intrinsic value	$ 260
Exercisable Aggregate intrinsic value	$ 260	$ 0

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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The number of shares into which fully or partially vested stock options outstanding as of the balance sheet date can be currently converted under the option plan.

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The weighted-average price as of the balance sheet date at which grantees can acquire the shares reserved for issuance on vested portions of options outstanding and currently exercisable under the stock option plan.

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Weighted average remaining contractual term for vested portions of options outstanding and currently exercisable or convertible, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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The number of shares under options that were cancelled during the reporting period as a result of occurrence of a terminating event specified in contractual agreements pertaining to the stock option plan.

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

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The number of shares reserved for issuance under stock option agreements awarded under the plan that validly exist and are outstanding as of the balance sheet date, including vested options.

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Weighted average remaining contractual term for option awards outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Weighted average price at which option holders acquired shares when converting their stock options into shares.

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Weighted average price at which grantees could have acquired the underlying shares with respect to stock options that were terminated.

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Number of share options (or share units) exercised during the current period.

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