Commitments and Contingencies - Narrative (Details) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013	Dec. 31, 2013
Commitments And Contingencies [Line Items]
Operating ground lease expense	$ 91,000	$ 42,000	$ 175,000	$ 84,000
Loss Contingency, Pending Claims, Number	0		0
Letter of credit obligations	8,100,000		8,100,000
Development in Process	329,685,000		329,685,000		209,187,000
Construction in Progress [Member]
Commitments And Contingencies [Line Items]
Number of Real Estate Properties	17		17
Leasable space of buildings	5,700,000		5,700,000
Anticipated aggregate investment	467,300,000		467,300,000
Deferred Costs, Leasing, Gross	10,800,000		10,800,000
Development Not Yet Commenced [Member]
Commitments And Contingencies [Line Items]
Land and building improvements	10,500,000		10,500,000
Land Held for Development [Member]
Commitments And Contingencies [Line Items]
Purchase Commitment, Remaining Minimum Amount Committed	82,800,000		82,800,000
Maximum [Member]
Commitments And Contingencies [Line Items]
Potential payments for tenant allowances	$ 40,100,000		$ 40,100,000