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Share-based Compensation - Additional Information (Details)
$ / shares in Units, fungible_unit in Millions
1 Months Ended 3 Months Ended 6 Months Ended 12 Months Ended
Aug. 31, 2014
shares
Jun. 30, 2018
USD ($)
unit / shares
unit
fungible_unit
shares
Jun. 30, 2017
USD ($)
Jun. 30, 2018
USD ($)
unit / shares
unit
fungible_unit
$ / shares
shares
Jun. 30, 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 $ 2,000,000 $ 3,200,000 $ 3,600,000      
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 2 months        
Remaining average contractual life of the options exercisable (in years)       3 years 2 months 15 days        
Total unrecognized compensation cost related to unvested stock awards   $ 4,900,000   $ 4,900,000        
Weighted average period for recognition of compensation cost related to unvested stock awards (in years)       1 year 3 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                
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%   10.00%        
Restricted Stock Awards                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Compensation expense       $ 6,251,350 9,809,749      
Total unrecognized compensation cost related to unvested stock awards   $ 15,200,000   $ 15,200,000        
Weighted average period for recognition of compensation cost related to unvested stock awards (in years)       1 year 10 months        
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       $ 9,800,000   $ 9,400,000    
Weighted average fair value of options granted during the period       $ 163,831 $ 9,905,986      
Awards granted (in shares) | shares       1,700 96,185      
Awards outstanding (in shares) | shares   3,291,616   3,291,616   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   $ 7,500,000   $ 7,500,000        
Weighted average period for recognition of compensation cost related to unvested stock awards (in years)       1 year 1 month        
Share-based compensation   $ 2,300,000 2,600,000 $ 9,100,000 $ 12,600,000      
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   27,030,000        
Fungible units per share (in fungible units per share) | unit / shares   3.74   3.74        
Shares that may be issued if equal to fungible units (shares) (less than) | shares   27,030,000   27,030,000        
Fungible units | fungible_unit   7.4   7.4        
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 1,900,000 $ 3,200,000 3,900,000      
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   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   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   $ 0 4,300,000 $ 0 6,300,000      
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   $ 100,000 $ 200,000 $ 2,100,000 $ 2,100,000      
Maximum percentage of the annual retainer fee, chairman fees and meeting fees that may be deferred by non-employee directors (percent)   100.00%   100.00%        
Awards granted (in shares) | shares       11,502        
Shares issued (in shares) | shares       9,332        
Awards outstanding (in shares) | shares   111,356   111,356        
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   110,045   110,045