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Stock-Based Compensation Plans (Details 5) - USD ($)
$ / shares in Units, $ in Thousands
6 Months Ended
Jun. 30, 2017
Jun. 30, 2016
Additional disclosures    
Stock-based compensation expense $ 8,950 $ 8,045
Capitalized stock-based compensation cost $ 4,979 $ 6,052
Performance Shares    
Additional disclosures    
Grant date value (in dollars per share) $ 179.07  
Restricted stock and restricted stock units    
Additional disclosures    
Unrecognized compensation cost for unvested restricted stock $ 37,923  
Weighted average period for recognition of unrecognized compensation cost 3 years 9 months 18 days