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Share-Based Compensation - Restricted Stock, Summary of Other Information (Details) - USD ($)
$ / shares in Units, $ 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]      
Weighted average remaining vesting period (years) 2 years 8 months 12 days    
Restricted Stock      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Granted (in shares) 0    
Weighted average grant-date fair value of restricted stock granted (in dollars per share) $ 0.00 $ 34.14 $ 30.30
Total fair value of stock awards vested during period $ 690 $ 311 $ 123
Weighted average remaining vesting period (years) 2 years 6 months