Investment in Unconsolidated Joint Ventures Balance Sheet of Unconsolidated Joint Ventures (Details) (USD $)	Dec. 31, 2013	Dec. 31, 2012
Schedule of Equity Method Investments [Line Items]
Real estate, net	$ 2,316,795,000	$ 1,562,717,000
Other assets	1,048,000	543,000
Total Assets	2,925,501,000	1,906,611,000
Mortgage notes payable	1,097,493,000	605,889,000
Other Liabilities	188,921,000	82,716,000
Total liabilities and partners' equity	2,925,501,000	1,906,611,000
Equity Method Investee [Member]
Schedule of Equity Method Investments [Line Items]
Cash	12,082
Restricted cash	5,846
Real estate, net	822,591
Intangible assets, net	63,234
Other assets	21,930
Total Assets	925,683
Mortgage notes payable	671,843
Other Liabilities	37,195
Below Market Rents	21,187
Partners' equity	195,458
Total liabilities and partners' equity	925,683
Equity Method Investee [Member] | US Airways Building [Member]
Schedule of Equity Method Investments [Line Items]
Cash	2,471
Restricted cash	0
Real estate, net	49,176
Intangible assets, net	2,809
Other assets	3,145
Total Assets	57,601
Mortgage notes payable	13,777
Other Liabilities	1,143
Below Market Rents	0
Partners' equity	42,681
Total liabilities and partners' equity	57,601
Equity Method Investee [Member] | 7000 Central Park JV, LLC [Member]
Schedule of Equity Method Investments [Line Items]
Cash	179
Restricted cash	0
Real estate, net	49,852
Intangible assets, net	4,832
Other assets	4,147
Total Assets	59,010
Mortgage notes payable	30,000
Other Liabilities	1,687
Below Market Rents	0
Partners' equity	27,323
Total liabilities and partners' equity	59,010
Equity Method Investee [Member] | PKY CalSTRS Austin, LLC [Member]
Schedule of Equity Method Investments [Line Items]
Cash	9,432
Restricted cash	5,846
Real estate, net	723,563
Intangible assets, net	55,593
Other assets	14,638
Total Assets	809,072
Mortgage notes payable	628,066
Other Liabilities	34,365
Below Market Rents	21,187
Partners' equity	125,454
Total liabilities and partners' equity	$ 809,072