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Stock-Based Compensation Stock-Based Compensation Expense and Related Tax Benefit (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Share-based Compensation [Abstract]      
Stock options $ 2,695 $ 2,357 $ 2,648
Restricted stock units 17,738 14,723 10,735
Unrestricted stock awards 974 955 706
Phantom stock units 1,747 1,077 0
Total stock-based compensation 23,154 19,112 14,089
Related tax benefit $ 5,034 $ 4,927 $ 4,228