Financial Instruments and Fair Values - Schedule of the aggregate carrying value of debt and estimates of fair value (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Interest rate swaps included in accounts payable and accrued expenses	$ 5,243	$ 436
Carrying Value | Revolving Credit Facility | Term Loan
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	264,147	263,662
Carrying Value | Fixed rate mortgage debt
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	608,567	717,164
Carrying Value | Senior unsecured notes - Exchangeable | Senior unsecured notes - Exchangeable
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	247,930	244,739
Carrying Value | Senior unsecured notes - Series A, B, C, D, E and F
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	798,289	463,156
Estimated Fair Value | Revolving Credit Facility | Term Loan
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	265,000	265,000
Estimated Fair Value | Fixed rate mortgage debt
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	597,424	707,300
Estimated Fair Value | Senior unsecured notes - Exchangeable | Senior unsecured notes - Exchangeable
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	250,625	275,723
Estimated Fair Value | Senior unsecured notes - Series A, B, C, D, E and F
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	795,662	460,352
Estimated Fair Value | Level 1 | Revolving Credit Facility | Term Loan
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	0	0
Estimated Fair Value | Level 1 | Fixed rate mortgage debt
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	0	0
Estimated Fair Value | Level 1 | Senior unsecured notes - Exchangeable | Senior unsecured notes - Exchangeable
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	0	0
Estimated Fair Value | Level 1 | Senior unsecured notes - Series A, B, C, D, E and F
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	0	0
Estimated Fair Value | Level 2 | Revolving Credit Facility | Term Loan
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	0	0
Estimated Fair Value | Level 2 | Fixed rate mortgage debt
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	0	0
Estimated Fair Value | Level 2 | Senior unsecured notes - Exchangeable | Senior unsecured notes - Exchangeable
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	250,625	275,723
Estimated Fair Value | Level 2 | Senior unsecured notes - Series A, B, C, D, E and F
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	0	0
Estimated Fair Value | Level 3 | Revolving Credit Facility | Term Loan
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	265,000	265,000
Estimated Fair Value | Level 3 | Fixed rate mortgage debt
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	597,424	707,300
Estimated Fair Value | Level 3 | Senior unsecured notes - Exchangeable | Senior unsecured notes - Exchangeable
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	0	0
Estimated Fair Value | Level 3 | Senior unsecured notes - Series A, B, C, D, E and F
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	795,662	460,352
Interest rate swaps
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Interest rate swaps included in accounts payable and accrued expenses	5,300
Interest rate swaps | Carrying Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Interest rate swaps included in prepaid expenses and other assets	2,536	0
Interest rate swaps included in accounts payable and accrued expenses	5,243	436
Interest rate swaps | Estimated Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Interest rate swaps included in prepaid expenses and other assets	2,536	0
Interest rate swaps included in accounts payable and accrued expenses	5,243	436
Interest rate swaps | Estimated Fair Value | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Interest rate swaps included in prepaid expenses and other assets	0	0
Interest rate swaps included in accounts payable and accrued expenses	0	0
Interest rate swaps | Estimated Fair Value | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Interest rate swaps included in prepaid expenses and other assets	2,536	0
Interest rate swaps included in accounts payable and accrued expenses	5,243	436
Interest rate swaps | Estimated Fair Value | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Interest rate swaps included in prepaid expenses and other assets	0	0
Interest rate swaps included in accounts payable and accrued expenses	$ 0	$ 0