Disclosure of Fair Value of Financial Instruments (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Mortgage Loans | Carrying Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long term debt	$ 396,690	$ 395,202
Mortgage Loans | Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long term debt	396,930	397,167
Unsecured Notes | Carrying Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long term debt	2,632,089	2,285,698
Unsecured Notes | Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long term debt	$ 2,722,758	$ 2,295,699