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Share-Based Compensation and Capital Stock - Summary Of Activity Related To Restricted Stock Grants (Details) - Restricted Stock - USD ($)
$ / shares in Units, $ in Thousands
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Restricted shares granted (in shares) 101,325 175,644 204,333
Weighted average grant date fair value (in dollars per share) $ 81.21 $ 61.84 $ 51.53
Aggregate grant date fair value $ 8,229 $ 10,862 $ 10,529
Restricted shares forfeited (in shares) 46,785 30,375 28,996
Fair value of shares vested $ 8,025 $ 12,616 $ 7,506
Minimum      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Vesting service period of shares granted 12 months 12 months 12 months
Maximum      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Vesting service period of shares granted 48 months 48 months 48 months