Fair Value of Assets and Liabilities (Details 2) (USD $) In Thousands, unless otherwise specified	12 Months Ended					12 Months Ended	0 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2013 Sale of properties Office property property	Dec. 31, 2012 Florence, KY Maximum	Dec. 31, 2013 Florence, KY Acquisition Office property	Feb. 14, 2014 Florence, KY Acquisition Office property Subsequent event	Dec. 31, 2013 Nonrecurring Total	Dec. 31, 2013 Nonrecurring Significant Unobservable Inputs (Level 3)	Dec. 31, 2012 Nonrecurring Significant Unobservable Inputs (Level 3) Florence, KY Acquisition Office property
Non-Recurring Fair Value Measurements
Properties held for sale	$ 1,380,927	$ 1,311,202						$ 14,560	$ 14,560
Additional purchase consideration								1,231	1,231	273
Number of properties for which a loss on asset impairment was recognized				2
Additional purchase consideration entitled to be paid to the seller, based upon the property's 2013 real estate tax assessment					1,800
Acquisition related costs	2,439	1,614	3,504			958
Additional purchase consideration paid to the seller							$ 1,231