Real Estate Investments Real Estate Investments (Purchase Price of Acquired Properties) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended			39 Months Ended
	Dec. 31, 2012 property	Dec. 31, 2011 property	Dec. 31, 2010 property	Dec. 31, 2012 property
Real Estate [Abstract]
Number of properties purchased	7	5	4	16
Business Acquisition, Cost of Acquired Entities Throughout Period, Purchase Price	$ 226,527	$ 57,926	$ 66,250	$ 350,703