Commitments and Contingencies - Supply Commitments (Details) $ in Thousands, ft² in Millions	Dec. 31, 2015 USD ($) ft² bldg	Dec. 31, 2014 USD ($)
Supply Commitment [Line Items]
Development in progress	$ 360,948	$ 277,411
Deferred leasing costs, gross	$ 229,798	$ 215,714
Construction in Progress [Member]
Supply Commitment [Line Items]
Number of buildings | bldg	27
Leaseable square feet (unaudited) | ft²	6.8
Anticipated aggregate investment	$ 672,000
Deferred leasing costs, gross	16,100
Building and land parcels [Member]
Supply Commitment [Line Items]
Remaining amount committed or obligated to pay for the benefit of current or future tenants	42,000
Tenant Improvements [Member]
Supply Commitment [Line Items]
Supply Commitment, Remaining Maximum Amount Committed	$ 53,500