Supplemental Disclosure of Cash Flow Information (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2011 The Brixton [Member]	Oct. 17, 2011 The Brixton [Member]		Dec. 31, 2012 The Park at Crossroads [Member]	Aug. 28, 2012 The Park at Crossroads [Member]
Business Acquisition [Line Items]
Dividends declared but not paid	$ 12,178		$ 10,149		$ 7,659
Issuance of shares for share-based compensation	0		1,916		1,490
Net change in accounts payable related to fixed asset additions	14,360		1,362		97
Net change in accounts payable and security deposits related to disposition of operating properties	(890)		(638)		(797)
Net change in accounts payable and security deposits related to acquisition of operating properties	1,800		1,072		463
Mortgage loan assumed	28,000	[1]	27,589	[2]	12,892	[3]		12,900	[4]		27,600	[4]
Assumed loan	$ 28,000	[4],[5],[6]	$ 27,589	[4]	$ 12,892	[4]	$ 12,300	$ 12,300		$ 24,900	$ 24,900
Interest rate to determine fair value			3.10%		4.50%

[1] Principal balance on loan assumed in 2013 approximated fair value at time of acquisition.

[2] Fair value amount of loan assumed in 2012 at time of acquisition. The principal balance at time of acquisition was $24.9 million. Fair value was determined based on an interest rate of 3.1%.

[3] Fair value amount of loan assumed in 2011 at time of acquisition. The principal balance at time of acquisition was $12.3 million. Fair value was determined based on an interest rate of 4.5%.

[4] Fair value was equal to principal amount of loan assumed in 2013 at the time of acquisition.

[5] Fair value amount of loan assumed in 2011 at the time of acquisition; actual principal amount of loan assumed was $12.3 million.

[6] Fair value amount of loan assumed in 2012 at the time of acquisition; actual principal amount of loan assumed was