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Summary of Significant Accounting Policies - Equity-Based Compensation, Taxes, Derivatives (Details) - USD ($)
12 Months Ended 36 Months Ended
Dec. 31, 2017
Dec. 31, 2014
Dec. 31, 2013
Income Tax Disclosure      
Percentage of annual REIT taxable income intended to be distributed to stockholders 100.00%    
Income tax expense $ 0    
Restricted Stock Units      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Vesting period of restricted share units (RSUs)   3 years 3 years
Restricted Stock Units | Minimum      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Vesting period of restricted share units (RSUs)     1 year
Restricted Stock Units | Maximum      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Vesting period of restricted share units (RSUs)     3 years