Financial Instruments and Fair Values - Schedule of the aggregate carrying value of debt and estimates of fair value (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Interest rate swaps included in accounts payable and accrued expenses	$ 5,591	$ 1,922
Carrying Amount [Member] | Revolving credit facility [Member] | Unsecured revolving credit facility [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value		35,192
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	262,927	262,545
Carrying Amount [Member] | Mortgages [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	759,016	747,661
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	241,474	238,208
Carrying Amount [Member] | Senior Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	348,914	348,810
Fair Value [Member] | Revolving credit facility [Member] | Unsecured revolving credit facility [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value		40,000
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	755,640	752,350
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	282,435	261,563
Fair Value [Member] | Senior Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	339,274	344,501
Fair Value [Member] | Fair Value, Inputs, Level 1 [Member] | Revolving credit facility [Member] | Unsecured revolving credit facility [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value		0
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] | Unsecured revolving credit facility [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value		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	282,435	261,563
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] | Unsecured revolving credit facility [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value		40,000
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	755,640	752,350
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	339,274	344,501
Interest rate swaps [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Interest rate swaps included in accounts payable and accrued expenses	5,100
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	614
Interest rate swaps included in accounts payable and accrued expenses	5,591	1,922
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	614
Interest rate swaps included in accounts payable and accrued expenses	5,591	1,922
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
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	614
Interest rate swaps included in accounts payable and accrued expenses	5,591	1,922
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
Interest rate swaps included in accounts payable and accrued expenses	$ 0	$ 0