Annual report pursuant to Section 13 and 15(d)

Shareholders' Equity Stock Options and Net Income per Share - Employee Stock Purchase Plan (Details)

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Shareholders' Equity Stock Options and Net Income per Share - Employee Stock Purchase Plan (Details) (USD $)
In Thousands, except Share data, unless otherwise specified
12 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Schedule of Employee Stock Purchase Plan (ESPP) Disclosures [Line Items]      
Share-based compensation $ 6,050 $ 5,971 $ 6,284
Employee Stock Purchase Plan [Member]
     
Schedule of Employee Stock Purchase Plan (ESPP) Disclosures [Line Items]      
Number of shares authorized under the plan 421,122    
Common stock issued under employee stock purchase plan (in shares) 8,846 9,122 8,142
Weighted average price of shares purchased (dollars per share) $ 29.26 $ 27.20 $ 23.89
Purchase Period for Employee Stock Purchase Plan 6 months    
Weighted Average Grant Date Fair Value $ 4.47 $ 5.79 $ 3.93
Share-based compensation $ 40 $ 53 $ 32