Commitments and Contingencies Commitments and Contingencies - Supply Commitments (Details) (USD $)	Sep. 30, 2014	Dec. 31, 2013
Supply Commitment [Line Items]
Development in Process	$ 250,506,000	$ 209,187,000
Construction in Progress [Member]
Supply Commitment [Line Items]
Number of Real Estate Properties	22
Area of Real Estate Property	4,700,000
Total anticipated development cost	428,700,000
Deferred Costs, Leasing, Gross	6,600,000
Development Not Yet Commenced [Member]
Supply Commitment [Line Items]
Total anticipated development cost	20,400,000
Buildings and land parcels [Member]
Supply Commitment [Line Items]
Remaining amount committed or obligated to pay for the benefit of current or future tenants	12,800,000
Maximum [Member] \| Tenant Improvements [Member]
Supply Commitment [Line Items]
Remaining amount committed or obligated to pay for the benefit of current or future tenants	$ 52,100,000

For an unclassified balance sheet, this element represents costs incurred by the lessor that are (a) costs to originate a lease incurred in transactions with independent third parties that (i) result directly from and are essential to acquire that lease and (ii) would not have been incurred had that leasing transaction not occurred and (b) certain costs directly related to specified activities performed by the lessor for that lease. Those activities are: evaluating the prospective lessee's financial condition; evaluating and recording guarantees, collateral, and other security arrangements; negotiating lease terms; preparing and processing lease documents; and closing the transaction. This amount is before considering accumulated amortization representing the periodic charge to earnings to recognize the deferred costs over the term of the related lease.

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The floor amount as of the balance sheet date that the entity must expend to satisfy the terms of disclosed arrangements (excluding long-term commitments) in which the entity must commit resources to supply goods or services to one or more customers.

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