Fair Value Measurements (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Value Measurements
Mortgage loans receivable	$ 39,299	$ 53,081
Marketable debt securities		6,485	[1]
Bonds payable	2,635	3,200
Bank borrowings	115,500	56,000
Senior unsecured notes	185,800	100,000
Earn-out liabilities	6,744	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		100.00%
Discount rate used to value earn out liabilities (as a percent)	6.60%	6.80%
Senior unsecured notes
Value Measurements
Senior unsecured notes	185,800
Discount rate used to value future cash outflow (as a percent)		4.80%
Senior unsecured notes maturing prior to 2020
Value Measurements
Discount rate used to value future cash outflow (as a percent)	3.80%
Senior unsecured notes maturing in 2020 and beyond
Value Measurements
Discount rate used to value future cash outflow (as a percent)	4.30%
Carrying Value
Value Measurements
Mortgage loans receivable	39,299	53,081
Marketable debt securities		6,485
Bonds payable	2,635	3,200
Bank borrowings	115,500	56,000
Senior unsecured notes	185,800	100,000
Earn-out liabilities	6,744	6,305
Fair Value
Value Measurements
Bonds payable	2,635	3,200
Bank borrowings	115,500	56,000	[2]
Fair Value | Level 2
Value Measurements
Marketable debt securities		6,500
Fair Value | Level 3
Value Measurements
Mortgage loans receivable	44,939	61,844
Senior unsecured notes	194,838	101,223
Earn-out liabilities	$ 6,744	$ 6,305

[1] At 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 12. Transactions with Related Party for further discussion.

[2] On December 31, 2012 and 2011, we had $3,191 and $3,060 respectively, in straight-line rent receivable from a lessee that qualifies as a related party because the lessee's Chief Executive Officer is on our Board of Directors. See Note 12. Transactions with Related Party for further discussion.