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Share-Based Compensation - Fair Values for SARs and Stock Options Estimated on Grant Date Using Black-Scholes-Merton Option-Pricing Formula Which Incorporates Assumptions (Details) - USD ($)
$ / shares in Units, $ in Thousands
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]      
Weighted-average fair value of SARs and options granted (in usd per share) $ 27.31 $ 18.79 $ 31.22
Total intrinsic value of SARs converted and options exercised $ 7,156 $ 9,678 $ 14,697
Cash received for options exercised 0 0 30
Tax benefit related to share-based compensation $ 967 $ 1,171 $ 5,050
Weighted-average fair value of restricted stock shares and units granted (in usd per share) $ 79.96 $ 54.52 $ 96.52
Total fair value of restricted stock shares and units vested $ 10,355 $ 8,171 $ 7,696
Expected volatility 36.89% 37.47% 35.66%
Expected term (in years) 5 years 7 months 2 days 5 years 8 months 12 days 5 years 8 months 12 days
Risk-free rate 2.01% 1.32% 1.59%
Dividend yield 0.27% 0.38% 0.22%