Fair Value Measurements (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2012		Dec. 31, 2011
Fair Value Measurements
Mortgage loans receivable	$ 52,368		$ 53,081
Marketable securities	6,486	[1]	6,485	[1]
Bonds payable	2,635		3,200
Bank borrowings	73,000		56,000
Senior unsecured notes	100,000		100,000
Earn-out liabilities	6,414		6,305
Discount rate used to value future cash inflows of the mortgage loans receivable (as a percent)	6.00%		6.00%
Fair value of marketable debt securities as a percentage of quoted market price	100.25%		100.00%
Discount rate used to value earn out liabilities	6.75%		6.82%
Senior unsecured notes
Fair Value Measurements
Discount rate used to value future cash outflow (as a percent)			4.80%
5.74% senior unsecured term notes due January 14, 2019
Fair Value Measurements
Discount rate used to value future cash outflow (as a percent)	3.80%
4.80% senior unsecured term notes due July 20, 2021
Fair Value Measurements
Discount rate used to value future cash outflow (as a percent)	4.40%
Carrying Value
Fair Value Measurements
Mortgage loans receivable	52,368		53,081
Marketable securities	6,486		6,485
Bonds payable	2,635		3,200
Bank borrowings	73,000		56,000
Senior unsecured notes	100,000		100,000
Earn-out liabilities	6,414		6,305
Fair Value
Fair Value Measurements
Bonds payable	2,635		3,200
Bank borrowings	73,000		56,000
Fair Value | Level 2
Fair Value Measurements
Marketable securities	6,516		6,500
Fair Value | Level 3
Fair Value Measurements
Mortgage loans receivable	60,467		61,844
Senior unsecured notes	104,120		101,223
Earn-out liabilities	$ 6,414		$ 6,305

[1] At March 31, 2012 and December 31, 2011, we had a $6,500 face value investment in marketable securities issued by an entity that qualifies as a related party because the entity's Chief Executive Officer is on our Board of Directors. See Note 9. Transactions with Related Party for further discussion.