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Share-based Compensation - Additional Information (Details)
$ / shares in Units, fungible_unit in Millions
1 Months Ended 3 Months Ended 12 Months Ended
Aug. 31, 2014
shares
Mar. 31, 2018
USD ($)
unit / shares
unit
fungible_unit
$ / shares
shares
Mar. 31, 2017
USD ($)
shares
Dec. 31, 2017
USD ($)
shares
Dec. 31, 2016
shares
Jan. 01, 2008
shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Capitalized to assets associated with compensation expense related to our long-term compensation plans, restricted stock and stock options   $ 1,600,000 $ 1,600,000      
Stock options            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Period of commencement of option vesting, from date of grant (in years)   1 year        
Exercise price of options granted, low end of the range (in dollars per share) | $ / shares   $ 20.67        
Exercise price of options granted, high end of the range (in dollars per share) | $ / shares   $ 137.18        
Remaining weighted average contractual life of the options outstanding (in years)   3 years 5 months        
Remaining average contractual life of the options exercisable (in years)   2 years 10 months 15 days        
Total unrecognized compensation cost related to unvested stock awards   $ 6,700,000        
Weighted average period for recognition of compensation cost related to unvested stock awards (in years)   1 year 2 months        
Weighted average fair value of options granted during the period   $ 84,068   $ 3,816,652    
Stock options | Minimum            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Award expiration period (in years)   5 years        
Options vesting period (in years)   1 year        
Stock options | Maximum            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Award expiration period (in years)   10 years        
Options vesting period (in years)   5 years        
Class O LTIP Units [Member]            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Share Based Compensation Arrangement by Share Based Payment Award, Preferred Unit Distributions as a Percentage of Common Unit Distributions   10.00%        
Restricted Stock Awards            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Compensation expense   $ 3,134,975 9,809,749      
Total unrecognized compensation cost related to unvested stock awards   $ 18,100,000        
Weighted average period for recognition of compensation cost related to unvested stock awards (in years)   2 years        
Annual award vesting rate, low end of range (as a percent)   15.00%        
Annual award vesting rate, high end of range (as a percent)   35.00%        
Fair value of restricted stock vested during the period   $ 9,700,000   $ 9,400,000    
Weighted average fair value of options granted during the period   $ 3,237,006 $ 9,905,986      
Awards granted (in shares) | shares   33,450 96,185      
Awards outstanding (in shares) | shares   3,327,116   3,298,216 3,202,031  
LTIP units            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Weighted average fair value of options granted during the period   $ 20,600,000   $ 20,500,000    
Performance Shares            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Total unrecognized compensation cost related to unvested stock awards   $ 9,700,000        
Weighted average period for recognition of compensation cost related to unvested stock awards (in years)   1 year 2 months        
Share-based compensation   $ 6,900,000 $ 10,000,000      
Third Amendment and Restated 2005 Stock Option and Incentive Plan            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Maximum fungible units that may be granted (in shares) | unit   27,030,000        
Fungible units per share (in fungible units per share) | unit / shares   3.74        
Shares that may be issued if equal to fungible units (shares) (less than) | shares   27,030,000        
Fungible units | fungible_unit   7.3        
Third Amendment and Restated 2005 Stock Option and Incentive Plan | Stock options            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Compensation expense   $ 1,600,000 2,000,000      
Stock options, stock appreciation rights and other awards            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Fungible units per share (in fungible units per share) | unit / shares   0.73        
Award expiration period (in years)   5 years        
All other awards            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Fungible units per share (in fungible units per share) | unit / shares   1.0        
Award expiration period (in years)   10 years        
2014 Outperformance Plan            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Compensation expense     2,100,000      
Capitalized to assets associated with compensation expense related to our long-term compensation plans, restricted stock and stock options   $ 27,900,000        
LTIP units earned (in shares) | shares 610,000          
Award period (in years) 3 years          
Maximum award to be earned, if performance reaches maximum threshold, first performance period 0.333          
Maximum award to be earned, if performance reaches maximum threshold, second performance period 0.667          
2014 Outperformance Plan | Vesting on August 31, 2017            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Percentage of units vested 50.00%          
2014 Outperformance Plan | Vesting on August 31, 2018            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Percentage of units vested 50.00%          
Deferred Stock Compensation Plan for Directors            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Compensation expense   $ 2,200,000 $ 1,900,000      
Maximum percentage of the annual retainer fee, chairman fees and meeting fees that may be deferred by non-employee directors (percent)   100.00%        
Awards granted (in shares) | shares   10,211        
Shares issued (in shares) | shares   9,266        
Awards outstanding (in shares) | shares   110,064        
Employee Stock Purchase Plan            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Shares of common stock available for issuance (shares) | shares           500,000
Duration of each offering period starting the first day of each calendar quarter (in months)   3 months        
Discount from market price   85.00%        
Shares of common stock issued (shares) | shares   107,193