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Incentive Stock Plans - Summary of Additional Information for Stock Options (Details) - Stock Options - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Intrinsic value of options exercised $ 1,993 $ 539 $ 773
Fair value of options vested 6,138 1,317 1,938
Cash received from exercise of options $ 4,751 $ 1,576 $ 2,117