Quarterly report pursuant to Section 13 or 15(d)

Net Income Per Share (Details)

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Net Income Per Share (Details) - USD ($)
$ / shares in Units, shares in Thousands, $ in Thousands
 3 Months Ended 6 Months Ended
Jun. 30, 2015
Jun. 30, 2014
Jun. 30, 2015
Jun. 30, 2014
Numerator [Abstract]        
Net income and comprehensive income $ 11,824 $ 17,178 $ 16,660 $ 27,379
Income allocated to participating securities (79)   (111)  
Numerator for basic and diluted income per share - net income $ 11,745 $ 17,178 $ 16,549 $ 27,379
Denominator [Abstract]        
Denominator for basic income per share - weighted-average shares 30,783 30,925 30,726 30,834
Denominator for diluted income per share - adjusted weighted-average shares 31,104 31,408 31,088 31,364
Basic income per share (dollars per share) $ 0.38 $ 0.56 $ 0.54 $ 0.89
Diluted income per share (dollars per share) $ 0.38 $ 0.55 $ 0.53 $ 0.87
Total number anti-dilutive options, non-vested shares, and performance shares excluded from income per diluted share computation     118 201
Stock Option [Member]        
Denominator [Abstract]        
Effect of dilutive stock options and non-vested shares 291 442 327 481
Total number anti-dilutive options, non-vested shares, and performance shares excluded from income per diluted share computation     97 182
Key Employee Performance Share Based Plan [Member]        
Denominator [Abstract]        
Effect of dilutive stock options and non-vested shares 30 41 35 49
Total number anti-dilutive options, non-vested shares, and performance shares excluded from income per diluted share computation     21 19