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Fair Value of Financial Instruments - Fair Value of Certain Financial Assets and Liabilities (Details) - USD ($)
$ in Thousands
Sep. 30, 2017
Dec. 31, 2016
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Carrying value of debt $ 940,805 $ 920,539
Carrying Amount    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Carrying value of debt 940,805 920,539
Fair Value    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Fair value of debt $ 951,552 $ 906,156