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Summary of Significant Accounting Policies - Debt Issuance Costs (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Amortization of deferred financing fees    
Amortization expense in 2018 $ 4,778  
Amortization expense in 2019 4,374  
Amortization expense in 2020 3,481  
Amortization expense in 2021 3,366  
Amortization expense in 2022 1,523  
Amortization expense thereafter 15,600  
Unsecured Term Loans, Senior Notes, and Mortgage Notes Payable    
Debt Instrument [Line Items]    
Deb issuance costs, gross 39,821 $ 49,331
Accumulated amortization, debt issuance costs gross 13,085 17,560
Revolving Credit Facility    
Debt Instrument [Line Items]    
Deb issuance costs, gross 17,170 10,980
Accumulated amortization, debt issuance costs gross $ 10,784 $ 9,039