Earnings per share (Details)	3 Months Ended	6 Months Ended
Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Earnings per share
Weighted average common share-basic	18,827,452	18,110,607	18,751,573	18,024,913
Effect of diluted securities:
Unexercised stock options net of treasury share repurchase	388,532	430,613	417,367
Weighted average common shares-diluted	19,215,984	18,541,220	19,168,940	18,024,913
Common stock equivalents
Antidilutive Securities Excluded from Computation of Earnings Per Share
Outstanding options not included in diluted earnings per share				350,233
Options to purchase common stock
Antidilutive Securities Excluded from Computation of Earnings Per Share
Outstanding options not included in diluted earnings per share	796,851	1,601,560	768,269	1,594,274

Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) or earnings per unit (EPU) in the future that were not included in the computation of diluted EPS or EPU because to do so would increase EPS or EPU amounts or decrease loss per share or unit amounts for the period presented.

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-Name Accounting Standards Codification

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Reference 5: http://www.xbrl.org/2003/role/presentationRef

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-Number 07-4

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Reference 6: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Diluted Earnings Per Share

-URI http://asc.fasb.org/extlink&oid=6510752

Reference 7: http://www.xbrl.org/2003/role/presentationRef

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-Name Accounting Standards Codification

-Topic 260

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+ Details

- Definition

The average number of shares or units issued and outstanding that are used in calculating diluted EPS or earnings per unit (EPU), determined based on the timing of issuance of shares or units in the period.

+ References+ Details

- Definition

Number of [basic] shares or units, after adjustment for contingently issuable shares or units and other shares or units not deemed outstanding, determined by relating the portion of time within a reporting period that common shares or units have been outstanding to the total time in that period.

+ References

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+ Details