Commitments and Contingencies (Details) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Loss Contingencies [Line Items]
Letter of credit, renewal period			1 year
Letter of Credit, July 2014 [Member]
Loss Contingencies [Line Items]
Letters of credit outstanding	$ 400,000		$ 400,000
Tenant Audits and Disputes [Member]
Loss Contingencies [Line Items]
Tenant audit dispute expense	300,000	0	600,000	0
Unsecured Debt [Member] | $500 Million Unsecured Line of Credit [Member]
Loss Contingencies [Line Items]
Face amount of debt instrument	500,000,000		500,000,000
Non-Incremental Capital Expenditures [Member]
Loss Contingencies [Line Items]
Potential obligations for tenant improvements	63,400,000		63,400,000
Incremental Capital Expenditures [Member]
Loss Contingencies [Line Items]
Potential obligations for tenant improvements	$ 16,900,000		$ 16,900,000