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Debt - Schedule of Debt Covenants (Details)
$ in Millions
 12 Months Ended
Dec. 31, 2017
USD ($)
Line of Credit Facility [Line Items]  
Percent of net proceeds from future equity issuances 75.00%
Line Of Credit Facility Covenant  
Line of Credit Facility [Line Items]  
Maximum leverage ratio (as a percent) 0.60
Minimum fixed charge coverage ratio 1.50
Minimum tangible net worth $ 1,910
Secured recourse indebtedness 45.00%
Line Of Credit Facility Covenant Actual Results  
Line of Credit Facility [Line Items]  
Maximum leverage ratio (as a percent) 0.246
Minimum fixed charge coverage ratio 4.42
Minimum tangible net worth $ 2,600
Secured recourse indebtedness 21.40%