Investment in Unconsolidated Joint Ventures - Balance Sheet of Unconsolidated Joint Ventures (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Schedule of Equity Method Investments [Line Items]
Real estate, net	$ 3,024,271	$ 2,316,795
Other assets	1,228	1,298
Total Assets	3,704,714	2,925,501
Mortgage debt	1,339,450	1,097,493
Other liabilities	202,413	188,921
Total liabilities & partners' equity	3,704,714	2,925,501
Equity Method Investee
Schedule of Equity Method Investments [Line Items]
Cash	1,364	12,082
Restricted cash	269	5,846
Real estate, net	96,164	822,591
Intangible assets, net	9,235	63,234
Other assets	2,923	21,930
Total Assets	109,955	925,683
Mortgage debt	43,441	671,843
Other liabilities	1,931	58,382
Partners' equity	64,583	195,458
Total liabilities & partners' equity	109,955	925,683
Equity Method Investee | US Airways Building
Schedule of Equity Method Investments [Line Items]
Cash	146	2,471
Restricted cash	0	0
Real estate, net	47,632	49,176
Intangible assets, net	5,078	2,809
Other assets	824	3,145
Total Assets	53,680	57,601
Mortgage debt	13,441	13,777
Other liabilities	370	1,143
Partners' equity	39,869	42,681
Total liabilities & partners' equity	53,680	57,601
Equity Method Investee | 7000 Central Park JV, LLC
Schedule of Equity Method Investments [Line Items]
Cash	1,218	179
Restricted cash	269	0
Real estate, net	48,532	49,852
Intangible assets, net	4,157	4,832
Other assets	2,099	4,147
Total Assets	56,275	59,010
Mortgage debt	30,000	30,000
Other liabilities	1,561	1,687
Partners' equity	24,714	27,323
Total liabilities & partners' equity	56,275	59,010
Equity Method Investee | PKY CalSTRS Austin, LLC
Schedule of Equity Method Investments [Line Items]
Cash	0	9,432
Restricted cash	0	5,846
Real estate, net	0	723,563
Intangible assets, net	0	55,593
Other assets	0	14,638
Total Assets	0	809,072
Mortgage debt	0	628,066
Other liabilities	0	55,552
Partners' equity	0	125,454
Total liabilities & partners' equity	$ 0	$ 809,072