Commitments and Contingencies (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014 executive_officer Guarantee	Dec. 31, 2013	Dec. 31, 2012
Commitments and Contingencies [Line Items]
Payments for capital improvements	$ 122,395	$ 447,571	$ 98,083
Number of guarantees outstanding	2
Number of executive officers entitled to severance benefits	4
Base Building Improvements [Member]
Commitments and Contingencies [Line Items]
Obligation for tenant improvements	1,384
Payment of the Base Building Improvement, Tenant Improvement Alloance, and Lease Commissions [Member]
Commitments and Contingencies [Line Items]
Obligation for tenant improvements	417
Byhalia, Mississippi [Member]
Commitments and Contingencies [Line Items]
Payments for capital improvements	$ 15,300