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Summary of Fair Value of Financial Instruments - Narrative (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Maximum maturity term of financial assets (less than) 90 days  
Note receivable, Carrying value $ 8,098 $ 8,098
Long-term debt, gross $ 826,236 $ 766,964
Minimum [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Notes receivable fair value variance from carrying value (as a percent) 1.00% 5.10%
Total indebtedness fair value variance from carrying value (as a percent) 94.40% 94.80%
Maximum [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Notes receivable fair value variance from carrying value (as a percent) 9.50% 16.20%
Total indebtedness fair value variance from carrying value (as a percent) 104.40% 104.70%