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Debt - Senior Unsecured Term Loan (Details)
 12 Months Ended
May 03, 2016
Dec. 31, 2017
USD ($)
Dec. 31, 2016
USD ($)
Line Of Credit Facility Leverage Range [Line Items]      
Outstanding principal balance   $ 944,434,000  
Line Of Credit Facility Covenant Actual Results      
Line Of Credit Facility Leverage Range [Line Items]      
Maximum leverage ratio (as a percent)   0.246  
Medium-term Notes | LIBOR      
Line Of Credit Facility Leverage Range [Line Items]      
Basis spread on variable rate   1.45%  
Interest incurred on the facility   $ 6,200,000 $ 1,300,000
Medium-term Notes | Less than or equal to 35% | LIBOR      
Line Of Credit Facility Leverage Range [Line Items]      
Basis spread on variable rate   1.45%  
Medium-term Notes | Greater than 35% but less than or equal to 45% | LIBOR      
Line Of Credit Facility Leverage Range [Line Items]      
Basis spread on variable rate   1.60%  
Medium-term Notes | Greater than 45% but less than or equal to 50% | LIBOR      
Line Of Credit Facility Leverage Range [Line Items]      
Basis spread on variable rate   1.75%  
Medium-term Notes | Greater than 50% but less than or equal to 55% | LIBOR      
Line Of Credit Facility Leverage Range [Line Items]      
Basis spread on variable rate   1.95%  
Medium-term Notes | Greater than 55% | LIBOR      
Line Of Credit Facility Leverage Range [Line Items]      
Basis spread on variable rate   2.20%  
Minimum | Medium-term Notes | LIBOR      
Line Of Credit Facility Leverage Range [Line Items]      
Basis spread on variable rate 1.45%    
Maximum | Medium-term Notes | LIBOR      
Line Of Credit Facility Leverage Range [Line Items]      
Basis spread on variable rate 2.20%    
Unsecured Term Loan Due May 2021 | Medium-term Notes      
Line Of Credit Facility Leverage Range [Line Items]      
Debt instrument, term (in years)   5 years  
Outstanding principal balance   $ 100,000,000  
Unsecured Term Loan Due April 2022 | Medium-term Notes      
Line Of Credit Facility Leverage Range [Line Items]      
Debt instrument, term (in years)   5 years