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Share-based Compensation and Non-Qualified Deferred Compensation Plan (Narrative) (Details)
$ / shares in Units, $ in Thousands
3 Months Ended
Mar. 31, 2019
USD ($)
shares
$ / shares
Mar. 31, 2018
USD ($)
$ / shares
May 17, 2018
shares
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value | $ / shares $ 98.58 $ 82.65  
Total compensation cost for option and share awards | $ $ 4,500    
Total capitalized compensation cost for option and share awards | $ 700 $ 900  
Share Awards and Vesting [Member]      
Total unrecognized compensation cost which is expected to be amortized | $ $ 25,100    
Expected amortized period of unrecognized compensation expected to be recognized for share-based compensation plans 3 years    
Fair value of shares vested | $ $ 18,900 $ 22,400  
Maximum [Member] | Share Awards and Vesting [Member]      
Vesting period, years 5 years    
Two Thousand Eighteen Share Incentive Plan [Member]      
Total common shares available | shares 7,600,000   9,700,000
Common shares To Full Value Award Conversion Ratio 3.45    
Value Of Option Right Or Other Award In The Fungible Unit Conversion | shares 1.0    
Full Value award in the common share conversion ratio | shares 1.0    
Common shares which could be granted pursuant to full value awards | shares 2,200,000