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Stockholders' Equity and Stock Plans - Dividends (Details) - USD ($)
$ / shares in Units, $ in Thousands
 12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Equity [Abstract]        
Cash dividends to common stockholders $ 5,390 $ 4,733 $ 3,970  
Cash dividends paid per common share $ 0.90 $ 0.80 $ 0.73  
Retained earnings $ 129,553 $ 116,502    
Stockholders' equity $ 214,473 $ 200,026 $ 180,887 $ 151,792
Period used to determine amount available for payment of dividends based on restriction 3 years      
Amount of retained earnings available for payment of dividends based on restriction $ 20,500      
Cash held $ 3,800