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Stock Based Compensation (Details) - Disclosure related to stock option plan - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]      
Intrinsic value of options exercised $ 1,270,521    
Cash received from options exercised 417 $ 767 $ 1,424
Tax benefit realized from options exercised $ 264 $ 117 $ 341