Financial Instruments and Fair Values - Schedule of the aggregate carrying value of debt and estimates of fair value (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Interest rate swaps included in accounts payable and accrued expenses	$ 436	$ 5,591
Carrying Amount [Member] | Revolving Credit Facility [Member] | Term Loan [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	263,662	262,927
Carrying Amount [Member] | Mortgages [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	717,164	759,016
Carrying Amount [Member] | Exchangeable notes [Member] | Exchangeable senior notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	244,739	241,474
Carrying Amount [Member] | Senior Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	463,156	348,914
Fair Value [Member] | Revolving Credit Facility [Member] | Term Loan [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	265,000	265,000
Fair Value [Member] | Mortgages [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	707,300	755,640
Fair Value [Member] | Exchangeable notes [Member] | Exchangeable senior notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	275,723	282,435
Fair Value [Member] | Senior Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	460,352	339,274
Fair Value [Member] | Fair Value, Inputs, Level 1 [Member] | Revolving Credit Facility [Member] | Term Loan [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	0	0
Fair Value [Member] | Fair Value, Inputs, Level 1 [Member] | Mortgages [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	0	0
Fair Value [Member] | Fair Value, Inputs, Level 1 [Member] | Exchangeable notes [Member] | Exchangeable senior notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	0	0
Fair Value [Member] | Fair Value, Inputs, Level 1 [Member] | Senior Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	0	0
Fair Value [Member] | Fair Value, Inputs, Level 2 [Member] | Revolving Credit Facility [Member] | Term Loan [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	0	0
Fair Value [Member] | Fair Value, Inputs, Level 2 [Member] | Mortgages [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	0	0
Fair Value [Member] | Fair Value, Inputs, Level 2 [Member] | Exchangeable notes [Member] | Exchangeable senior notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	275,723	282,435
Fair Value [Member] | Fair Value, Inputs, Level 2 [Member] | Senior Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	0	0
Fair Value [Member] | Fair Value, Inputs, Level 3 [Member] | Revolving Credit Facility [Member] | Term Loan [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	265,000	265,000
Fair Value [Member] | Fair Value, Inputs, Level 3 [Member] | Mortgages [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	707,300	755,640
Fair Value [Member] | Fair Value, Inputs, Level 3 [Member] | Exchangeable notes [Member] | Exchangeable senior notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	0	0
Fair Value [Member] | Fair Value, Inputs, Level 3 [Member] | Senior Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	460,352	339,274
Interest rate swaps [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Interest rate swaps included in accounts payable and accrued expenses	500
Interest rate swaps [Member] | Carrying Amount [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Interest rate swaps included in prepaid expenses and other assets	0	614
Interest rate swaps included in accounts payable and accrued expenses	436	5,591
Interest rate swaps [Member] | Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Interest rate swaps included in prepaid expenses and other assets	0	614
Interest rate swaps included in accounts payable and accrued expenses	436	5,591
Interest rate swaps [Member] | Fair Value [Member] | Fair Value, Inputs, Level 1 [Member]
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 [Member] | Fair Value [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Interest rate swaps included in prepaid expenses and other assets	0	614
Interest rate swaps included in accounts payable and accrued expenses	436	5,591
Interest rate swaps [Member] | Fair Value [Member] | Fair Value, Inputs, Level 3 [Member]
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