Fair Value Measurements (Details) (USD $)	6 Months Ended	12 Months Ended
	Jun. 30, 2014	Dec. 31, 2013
Fair value measurements
Mortgage loans receivable	$ 168,068,000	$ 165,444,000
Senior unsecured notes	251,633,000	255,800,000
Fair Value Inputs Level3 [Member] | Senior Unsecured Notes Maturing Prior To2020 [Member]
Fair value measurements
Discount rate (as a percent)	3.80%	3.95%
Fair Value Inputs Level3 [Member] | Senior Unsecured Notes Maturing Beyond2020 [Member]
Fair value measurements
Discount rate (as a percent)	3.95%	4.25%
Fair Value Inputs Level3 [Member] | Mortgage Receivables [Member]
Fair value measurements
Discount rate (as a percent)	8.50%	8.40%
Carrying Reported Amount Fair Value Disclosure [Member]
Fair value measurements
Mortgage loans receivable	168,068,000	165,444,000
Bonds payable	1,400,000	2,035,000
Bank borrowings	42,000,000	21,000,000
Senior unsecured notes	251,633,000	255,800,000
Estimate Of Fair Value Fair Value Disclosure [Member]
Fair value measurements
Bonds payable	1,400,000	2,035,000
Bank borrowings	42,000,000	21,000,000
Estimate Of Fair Value Fair Value Disclosure [Member] | Fair Value Inputs Level3 [Member]
Fair value measurements
Mortgage loans receivable	196,275,000	200,248,000
Senior unsecured notes	$ 260,980,000	$ 262,351,000