Commitments and Contingencies (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014
Long-term Purchase Commitment [Line Items]
Number of Properties	2
Costs Incurred to Date	549,130
Expected Costs to Complete	255,747	[1]
Wholly-owned — under development
Long-term Purchase Commitment [Line Items]
Number of Properties	1
Costs Incurred to Date	177,632
Purchase Commitment, Remaining Minimum Amount Committed	40,068
Average Ownership Stake	100.00%
Wholly-owned — redevelopment
Long-term Purchase Commitment [Line Items]
Number of Properties	1
Costs Incurred to Date	83,778
Purchase Commitment, Remaining Minimum Amount Committed	14,222
Average Ownership Stake	100.00%
Unconsolidated joint ventures
Long-term Purchase Commitment [Line Items]
Number of Properties	3
Costs Incurred to Date	225,013
Purchase Commitment, Remaining Minimum Amount Committed	172,155
Participating Loan Investment Steele Creek Denver Colorado [Member]
Long-term Purchase Commitment [Line Items]
Number of Properties	1
Costs Incurred to Date	62,707
Purchase Commitment, Remaining Minimum Amount Committed	29,302
Average Ownership Stake	0.00%

[1] Represents 100% of project costs incurred to date.