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Share-Based Compensation - Effect of Recording Share-Based Compensation Expense (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]      
Share-based compensation expense [1] $ 11,223 $ 7,879 $ 7,242
Income tax benefit 4,601 3,152 2,962
Share-based compensation expense, net of tax 6,622 4,727 4,280
Unrecognized compensation expense $ 13,266 $ 9,990 $ 8,644
Weighted-average amortization period remaining (in years) 1 year 3 months 10 days 1 year 4 months 1 year 4 months 7 days
[1] Comprised of restricted stock, restricted stock unit, and performance share awards expense.