Financial Instruments and Fair Values - Schedule of the aggregate carrying value of debt and estimates of fair value (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Interest rate swaps included in accounts payable and accrued expenses	$ 8,849	$ 13,330
Carrying Value | Revolving Credit Facility | Unsecured term loan facility
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	387,561	264,640
Carrying Value | Mortgage notes payable
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	775,929	605,542
Carrying Value | Senior unsecured notes - Series A, B, C, D, E, F, G and H
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	973,159	798,392
Estimated Fair Value | Revolving Credit Facility | Unsecured term loan facility
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	390,000	265,000
Estimated Fair Value | Mortgage notes payable
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	808,294	629,609
Estimated Fair Value | Senior unsecured notes - Series A, B, C, D, E, F, G and H
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	1,039,857	843,394
Estimated Fair Value | Level 1 | Revolving Credit Facility | Unsecured term loan facility
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	0	0
Estimated Fair Value | Level 1 | Mortgage notes payable
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, F, G and H
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 | Unsecured term loan facility
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	0	0
Estimated Fair Value | Level 2 | Mortgage notes payable
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 - Series A, B, C, D, E, F, G and H
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 | Unsecured term loan facility
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	390,000	265,000
Estimated Fair Value | Level 3 | Mortgage notes payable
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	808,294	629,609
Estimated Fair Value | Level 3 | Senior unsecured notes - Series A, B, C, D, E, F, G and H
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	1,039,857	843,394
Interest rate swaps
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Interest rate swaps included in accounts payable and accrued expenses	8,900
Interest rate swaps | Carrying Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Interest rate swaps included in accounts payable and accrued expenses	8,849	13,330
Interest rate swaps | Estimated Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Interest rate swaps included in accounts payable and accrued expenses	8,849	13,330
Interest rate swaps | Estimated Fair Value | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
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 accounts payable and accrued expenses	8,849	13,330
Interest rate swaps | Estimated Fair Value | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Interest rate swaps included in accounts payable and accrued expenses	$ 0	$ 0